Insularity and Expansion

In the context of great power politics, what is the relationship between insularity and expansion? We define insularity as being surrounded by water. An insular power would thus be the only great power on a large body of land that is surrounded on all sides by water.Footnote ² A continental power, on the other hand, would be a great power located on a large body of land that is also occupied by at least one other great power (Mearsheimer Reference Mearsheimer2014, 126).Footnote ³ We define expansion, in turn, as the extension of a state’s territorial control or political influence (Gilpin Reference Gilpin1981, 106).

If there is a received wisdom on the link between insularity and expansion, it is that insularity constrains expansion, primarily by making the conquest of other great powers exceedingly difficult (Jervis Reference Jervis1978, 189; Taliaferro Reference Taliaferro2000, 139; Van Evera Reference Van Evera1999, 121; Glaser and Kaufmann Reference Glaser and Kaufmann1998, 58). This argument is most clearly developed in the realist tradition which, as a body of work emphasizing states’ desire for power and security and the causal weight of material factors, has tended to be most attuned to the influence of geography in general and insularity in particular (for a partial exception, see Lake Reference Lake1999, 44-46). In this vein, defensive realism finds that insularity influences the severity of the security dilemma between great powers by affecting their ability to attack and conquer one another (Taliaferro Reference Taliaferro2000: 136-41). Here, being surrounded by water particularly advantages the defense relative to the offense. Robert Jervis lays out the key elements of the argument in his treatment of the security dilemma, offering that, “Anything that increases the amount of ground the attacker has to cross, or impedes his progress across it, or makes him more vulnerable while crossing, increases the advantage accruing to the defense. When states are separated by barriers that produce these effects, the security dilemma is eased, since both can have forces adequate for defense without being able to attack.” Large bodies of water such as oceans serve the same function in this respect: “Being hard to cross, they allow defense against superior numbers. The defender has merely to stay on his side of the barrier and so can utilize all the men he can bring up to it. The attacker’s men, however, can cross only a few at a time, and they are very vulnerable when doing so.” If all states were islands, each would thus be largely secure (Jervis Reference Jervis1978, 194–96; also Van Evera Reference Van Evera1998, 19; Glaser and Kaufmann Reference Glaser and Kaufmann1998, 64-66; Glaser Reference Glaser2010, 141).

Offensive realism converges with defensive realism on insularity’s essential defense-dominance (Blagden, Levy, and Thompson Reference Blagden, Levy and Thompson2011, 196). Here, the stopping power of water (Mearsheimer Reference Mearsheimer2014, 114-128)—the limits that large bodies of water place on states’ ability to project land power—inhibits insular powers from attacking great powers outside their regions. This explains why great powers can only aspire to regional hegemony despite the fact that they would be more powerful and secure as global hegemons. In doing so, insularity adds a defensive element to an international system otherwise primed for offense. Although less precise than either offensive or defensive realism, classical (Morgenthau Reference Morgenthau1963, 110-112) and neoclassical (Ripsman, Taliaferro, and Lobell Reference Ripsman, Taliaferro and Lobell2016, 41-42) realism take a similar approach, suggesting that insularity limits the external threats that great powers face and so reduces their need to expand in kind. Meanwhile, scholars utilizing insights from existing discussions of insularity to explain particular strategies by individual great powers echo these claims. Josef Joffe, for instance, contends that insularity “granted Britain that rarest gift of inter-state politics: immunity from direct attack,” pushing Britain to prefer “balancing [against great power threats] rather than conquest” (Joffe Reference Joffe1997, 102, 104). Similarly, Jennifer Lind argues that Japanese insularity reduced its fears of attack during the Cold War, leading it to underinvest in military power relative to its economic potential and forego efforts at overseas power projection (Lind Reference Lind2004, 104, 117).

Insularity and Expansion: The Limits of the Received Wisdom

In sum, the received wisdom holds that insularity is a constraint on expansion. We contend, by contrast, that this received wisdom is incomplete. First and foremost, the claim that insularity constrains expansion has difficulty accounting for insular powers’ behavior, with the United States’ record of expansion since 1945 posing a particular challenge. After all, as the insular power par excellence—surrounded by oceans on two sides, with weak neighbors to the north and south—the United States should be among the least likely of great powers to expand abroad. In fact, just the opposite has occurred.

Since World War II, the United States has built what Geir Lundestad terms an “empire by invitation,” projecting power overseas in geopolitically significant regions such as Western Europe, East Asia, and the Middle East (Lundestad Reference Lundestad1999). The effort has gone beyond simply maintaining a diplomatic and military footprint to hedge against regional disturbances. Instead, the United States has worked to control and structure regional dynamics in accordance with American interests. To do so, it has deployed large military forces abroad, committed substantial sums of money to overseas operations, involved itself heavily in regional diplomatic and economic affairs, and even risked war against capable states such as the Soviet Union, Iraq, and China (Jaffe Reference Jaffe1993; Trachtenberg Reference Trachtenberg1999; Layne Reference Layne2002; Lake Reference Lake2008, Reference Lake2009; Hoffman Reference Hoffman2013; Brooks and Wohlforth Reference Brooks and Wohlforth2016; Silove Reference Silove2016; Cooley and Nexon Reference Cooley and Nexon2020; Moller Reference Moller2020). Equally telling, the United States has increased its overseas presence over time, as NATO’s post-Cold War move into Eastern Europe and ongoing efforts to bolster the U.S. commitment in Asia illustrate (Sarotte Reference Sarotte2019a; Lind Reference Lind2014).

For sure, relatively little of the United States’ effort involved conquest, with much of its overseas presence negotiated with continental actors. Still, if the idea that insularity constrains expansion is to mean anything, we would not expect the United States to retain such an extensive presence abroad over such a lengthy period. Nor has the effort been entirely cooperative, with the United States frequently coercing other major powers such as Britain, France, Germany, the Soviet Union, and China in order to advance its overseas interests, often risking military confrontation along the way (Woods Reference Woods1990; Kingseed Reference Kingseed1995; Trachtenberg Reference Trachtenberg1999; Shifrinson Reference Shifrinson2018, chap. 5; Silove Reference Silove2016; Campbell and Sullivan Reference Campbell and Sullivan2019). These efforts are again difficult to explain if insularity mostly promotes restraint.

Neither can insular expansion be dismissed as an American phenomenon, as other insular powers have acted similarly. During its zenith in the nineteenth century, for example, the United Kingdom possessed a sizable fraction of global economic and military capabilities, and unrivalled command of the seas (Singer, Bremer, and Stuckey Reference Singer, Bremer, Stuckey and Russett1973; Rodger Reference Rodger2006). As an insular power able to control its own moats, the received wisdom would predict British restraint vis-à-vis other great powers. Yet, while it is true that the United Kingdom never sought to conquer the major states of continental Eurasia, it nevertheless expanded at their expense through a variety of channels. Thus, Britain challenged Russian claims in Central Asia, asserted dominance over the Yokohama Treaty Port that the U.S. Navy had opened in Japan, preempted France by annexing Egypt to ensure access to the Suez Canal, and competed with France and Germany for colonies in Africa—even risking near-wars with each in the late 1800s and early 1900s (Porter and Low Reference Porter and Low1999). Likewise, Japan expanded its footprint throughout East Asia in the late nineteenth and early twentieth centuries, not conquering other great powers but frequently challenging their interests—culminating in war against Russia. Again, such efforts are puzzling if insularity is constraining.Footnote ⁴

The record of insular power expansion also highlights a conceptual dilemma with existing research, in that current studies rely upon a circumscribed definition of what expansion entails. To date, scholars interested in insularity have tended to equate expansion with conquest, that is, one state forcibly seizing some or all of the territory held by another. This type of expansion is certainly important—indeed, it occupies a prominent place in European diplomatic history and IR theory. Still, it is not axiomatic that expansion is synonymous with conquest.

This point is captured in the literatures on hegemony, hierarchy, imperialism, and order. As scholars such as David Lake, John Ikenberry, and Daniel Nexon underscore, great powers have been able to structure and influence the policy choices of other actors while stopping short of conquest. This insight applies to the contemporary United States: in one recent treatment, Nexon and Alexander Cooley emphasize that “within broader international order we find an American hegemonic system … within which the United States directly orders and takes leadership of economic, security, and political relations” (Cooley and Nexon Reference Cooley and Nexon2020, 46; see also Lake Reference Lake2009, 82). To be clear, this body of research largely sidesteps the geopolitical factors that may enable expansion in order to focus on the economic, institutional, and normative factors undergirding the formation of different kinds of ordered relationships. Indeed, to the extent insularity enters the equation, research in this vein seems to largely accept the received wisdom of insularity as a constraint on expansion (Lake Reference Lake1999, 46). Still, the scholarly program as a whole clarifies that great powers can expand short of conquest by crafting spheres of influence—more or less formally defined geographic areas in which great powers dominate others’ strategic affairs and, by extension, exclude outside actors from similar influence over the same space (Lake Reference Lake1999, 28-29; Lake Reference Lake2009, 54; Jackson Reference Jackson2020).

Of course, the nature of the political relationships that characterize spheres of influence can vary, with some spheres characterized by mutually beneficial leader-subordinate relationships (Lake Reference Lake1993; Clark Reference Clark2009a, Reference Clark2009b) while others entail little more than strong states maintaining self-interested arrangements at the expense of the weak (Layne Reference Layne2006). At the limit, spheres of influence can even evolve into arrangements affecting the domestic politics of subordinate actors (Lake Reference Lake1999; Go Reference Go2011). Regardless of the form it takes, however, expansion via spheres of influence is still expansion, with the effort involving real costs and benefits for the sphere-builder.

In terms of costs, sphere-of-influence-building involves shaping others’ choices via statecraft short of brute force. Hence, it can require states to extend diplomatic and security commitments, deploy troops, and provide economic aid while risking conflict with competitors opposed to their expansion. On the benefits side, spheres can provide states greater leverage over their international environments than would otherwise be the case by fostering military quiescence, economic remuneration, and diplomatic fealty from those in one’s sphere. Given that conquest has become progressively less appealing (Schweller Reference Schweller2011; Fazal Reference Fazal2007) as weaponry has become more destructive (Mueller Reference Mueller1989), the economics of conquest less obvious,Footnote ⁵ nationalism more pronounced (Roshwald Reference Roshwald2000), and norms of territorial integrity more robust (Zacher Reference Zacher2001),Footnote ⁶ non-conquest methods of expansion such as spheres of influence are poised to be particularly relevant for contemporary world politics.

Insularity as Facilitator of Expansion

In tandem, the empirical problem posed by insular powers’ record of expansion and the theoretical problem in equating expansion with conquest suggest that existing scholarship linking insularity with non-expansion is incomplete. Rather than discard the received wisdom, we seek to reformulate and adapt its core insights. In the process, we draw on research implying that insular powers may enjoy advantages in great power politics—in particular, that insularity may facilitate power projection while reducing others’ tendency to counterbalance. While this research is not focused on expansion as such, we extend its insights to specifically consider its implications for insular power expansion.

Our starting premise is that although insularity cannot explain why great powers expand, it shapes their opportunity structure when they seek to expand.Footnote ⁷ More specifically, insular powers—like other great powers—can face a mix of security and non-security motives to expand that vary across time and space (Glaser Reference Glaser2010; Grynaviski Reference Grynaviski2018; Shifrinson Reference Shifrinson2018). Yet, because insularity—as the received wisdom emphasizes—makes the conquest of other great powers difficult,Footnote ⁸ insular powers are pushed to consider alternate ways of expanding. This is where spheres of influence come into play.

In turn, insularity provides great powers with two advantages in constructing spheres of influence. First, insular powers are free to roam: secure at home, they enjoy a margin of strategic error that allows them to focus on projecting power and influence abroad. Second, insular powers’ geographic remove makes them attractive security partners for states located in geopolitically crowded neighborhoods, increasing the demand for their presence abroad. Each mechanism has been flagged in previous research, but their combined impact in terms of facilitating expansion via spheres of influence has been overlooked. We treat each in turn.

Linking Insularity and the Onshore Distribution of Power to Expansion

Combined, the freedom to roam and the sterilizing effect of insularity can facilitate insular power expansion via spheres of influence. On the one hand, the freedom to roam allows insular powers to devote resources to expansion abroad: secure at home, they are able to project power and influence beyond their borders. Meanwhile, insularity’s sterilizing effect makes offshore powers less of a threat to continental powers than their neighbors. Hence, insular powers find themselves invited into other regions as security providers, gaining influence over continental states in the process. In tandem, these pathways create a space whereby insular powers are able to expand in ways short of conquest: they can leverage their extra resources and attractiveness as partners to gain access to other regions and cultivate spheres of influence.

Still, insular powers’ opportunity to expand by crafting spheres is not unlimited. Instead, we hypothesize that relative power—especially the onshore distribution of power in regions of interest—is likely to influence whether and when insular powers can play to their advantages and expand in the manner described. Put simply, the onshore distribution of power affects when insular powers are invited into a region, the influence they can exert there, and which (if any) states want them out. In turn, as the onshore distribution of power varies, so too does the capacity to create spheres of influence.

For the sake of theory development, we consider three distinct onshore distributions of power while holding an insular power’s strength constant. First, an insular power might face a region dominated by a local hegemon. In this scenario, an insular power’s ability to expand should be limited as the hegemon would aim to keep the insular power out; likewise, by virtue of the hegemon’s dominating regional politics, we further expect the hegemon’s neighbors to defer to its wishes. Reinforcing the situation, the insular power may be reluctant to expand in the first place as it may worry about the hegemon’s meddling in its own backyard.Footnote ¹⁵

Alternatively, consider onshore distributions of power that replicate what can be thought of as classic balance-of-power situations: circumstances in which at least two great powers are struggling for security vis-à-vis one another. This set of conditions—which could encompass bipolar, balanced multipolar, and unbalanced multipolar systems—should be most conducive to insular power expansion via spheres of influence. On one level, competition among continental powers means that at least one of them is likely to seek assistance from an insular power that, because of the freedom to roam and difficulty of conquering other powers, can contribute to the onshore great power competition without overly threatening the players. Put simply, regional great power politics creates an opening for an insular power to move onshore. At the same time, the insular power is well positioned to demand concessions to its interests from any continental powers that seek its backing. In this way, it can exploit balance of power dynamics to expand onshore and form a sphere of influence.

This logic further implies that an insular power’s space to expand via spheres of influence is likely to grow the more intensely that continental powers are threatened by their onshore peers. The presence or emergence of unbalanced multipolarity—where one continental great power looks poised to become a regional hegemon—seems especially favorable for insular power expansion. With relative power weighted in one continental state’s favor, unbalanced multipolar environments are likely to create a large demand for an insular power’s presence to offset the potential hegemon on the part of most or all other continental great powers threatened by domination. Likewise, owing to the clear and pressing nature of the threat, one expects menaced states to be willing to accede to an insular power’s demands. Combined, insular powers are poised to have multiple invitations onshore, significant bargaining leverage, and the possibility of creating a sphere of influence encompassing an array of continental great powers. That said, it follows that the potential hegemon would be especially focused on undermining the insular power’s sphere of influence and pushing it offshore. Thus, it is no accident that the United States 1) built its “empire by invitation” following World War II when the Soviet Union loomed as a potential hegemon that local states sought to resist, and 2) was opposed by the Soviet Union. Likewise, it is unsurprising from this perspective that the American presence in Asia is currently growing as Japan and other regional states eye a rising China warily while China—as the only challenger for regional hegemony – is increasingly ambivalent over the United States’ presence (Wuthnow Reference Wuthnow2018; Weiss Reference Weiss2019).

Finally, an insular power may face an onshore distribution without other great powers. In this scenario, an insular power is poised to face few obstacles to expansion of any kind. Indeed, even the received wisdom suggests that conquest might be feasible under such conditions as insular states that lack the capacity to conquer great powers might be sufficiently strong to dominate the relatively weak local actors involved. Local states may still invite insular powers onshore in order to gain their support in regional competitions, but—in practice—insular powers retain the option to expand either via spheres of influence or conquest as the imbalance of power in their favor reduces the costs of using force; either form of expansion would be possible. Similarly, the absence of other great powers may make it especially easy for insular powers to establish imperial relationships over local actors, whether formal empire as in the case of Britain in the nineteenth century or informal empire as in the case of the modern United States (Kohli Reference Kohli2020).

Overall, the feasibility of conquest in this scenario may help explain exceptions to the claim that insular powers expand through means other than conquest. For example, Japan built an overseas empire through conquest in the late nineteenth and early twentieth centuries. Consistent with our framework, Japan’s primary gains came in the parts of Asia (Taiwan, Korea, and a fragmenting China) where other great powers were absent.Footnote ¹⁶ Likewise, the relatively low cost of conquest absent other great powers might account for why Britain conquered large portions of Africa and Asia in the nineteenth century: although Britain confronted other great powers in the process, major conquests in Africa and Asia were predominantly at the expense of weak local actors rather than peer competitors (for details, see MacDonald Reference MacDonald2014).

Insularity in Action: American Grand Strategy

Without claiming to offer a complete theory of insular power expansion, we have thus far hypothesized why insular power expansion is possible without the direct conquest of other great powers, as well as the conditions under which such expansion may occur.Footnote ¹⁷ To showcase the plausibility of our claims, it is worth briefly considering the application of the argument to the United States, the insular power par excellence. Here, our framework neatly ties together a number of themes that are usually emphasized separately in the literature on American grand strategy.

Ultimately, it is hard to argue that the United States has not been expansionist. As noted earlier, since 1945 it has cultivated spheres of influence in Western Europe, East Asia, and the Middle East. Admittedly, the scope and nature of these spheres have varied over time and space. Nevertheless, the United States has generally embraced extensive security commitments to the most capable states in these areas and deployed large military forces to bolster its commitments. The United States has also worked to shape relations among states in its orbit in ways that redound to its benefit while seeking to deter threats from actors outside these arrangements. Collectively, this all adds up to a preponderant American role in these regions (Leffler Reference Leffler1992; Layne Reference Layne2006; Brooks and Wohlforth Reference Brooks and Wohlforth2016), with even once-skeptical scholars referring to the United States as a global hegemon after the Cold War (Posen Reference Posen2014; Mearsheimer Reference Mearsheimer2018; Walt Reference Walt2018).

The extent of this expansion presents a puzzle for the received wisdom, which has trouble explaining how and why an insular power such as the United States could successfully cultivate spheres of influence in several regions over a decades-long period. In contrast, our claim that insularity abets expansion through non-conquest means helps capture this trend. By our logic, insularity may not explain why the United States expands, but it neatly illuminates why the United States enjoys the capacity and opportunity to do so. In fact, several aspects of our argument are evident in postwar American grand strategy.

For one thing, the United States has enjoyed nearly unprecedented freedom to roam and has thus been able to invest extensively in power projection. During the Cold War, this involved forward-deployed forces in Europe and Asia to help deter Soviet aggression, alongside “expeditionary” forces suitable for rapid transport to global hotspots. Similarly, faced today with China’s rise, strategists are recalibrating the United States’ overseas presence, shifting military forces to Asia and acquiring capabilities optimized for power projection in the region (Hicks and Green Reference Hicks and Green2016; Mitre Reference Mitre2018). Along the way, the decades-long American investment in power projection has yielded “command of the commons”: the ability to unilaterally exploit the air, sea, and space domains while denying their use to others (Posen Reference Posen2003). Simply put, insularity has enabled the United States to focus on overseas contingencies without imperiling security at home.

Second, and despite its investment in power projection, the United States has been readily invited onshore in other regions while gaining substantial influence over partners’ foreign policies. One of the more striking features of American grand strategy has been the readiness with which other countries have sought out an American presence and encouraged U.S. inroads in their neighborhoods. Western European states, for instance, lobbied the United States to involve itself in European politics after World War II against the Soviet Union (Ireland Reference Ireland1981). After the Cold War, Eastern European states similarly called for NATO enlargement to gain the United States as an ally against Russia while Western European actors sought to keep the United States in the region to offset a newly reunified Germany (Goldgeier Reference Goldgeier1999; Sayle Reference Sayle2019; Sarotte Reference Sarotte2019b). Similar trends occurred in Asia—as local powers such as Japan sought out an American commitment to offset the Soviet Union and China (Nye Reference Nye1995; Samuels Reference Samuels2007)—and the Middle East—where states as varied as Israel, Iran, and Saudi Arabia have invited the United States into the region at different times to address local security problems (Bar-Siman-Tov, Hahn, and Schoenbaum Reference Bar-Siman-Tov, Hahn and Schoenbaum1998; Litwak Reference Litwak1984; Long Reference Long1985). Once committed, meanwhile, the United States has been able to influence local states’ security policies by stymying partners’ nuclear aspirations (Gavin Reference Gavin2015), shaping allied diplomatic and military policies (Trachtenberg Reference Trachtenberg1999; Rapp-Hooper Reference Rapp-Hooper2020), and blocking alternate security systems from forming (Zoellick Reference Zoellick, Leffler and Legro2011; Shifrinson Reference Shifrinson2020b). Along the way, states in the American orbit have worried that the United States would play to its insularity and abandon them, providing a potent source of U.S. bargaining leverage (Trachtenberg Reference Trachtenberg1999; Schuessler and Shifrinson Reference Schuessler and Shifrinson2019).Footnote ¹⁸ In sum, not only has the United States been invited into other regions—a finding consistent with our framework—but it has used this position to influence regional dynamics in a manner conducive to U.S. interests.

One might counter that the freedom to roam and invitations onshore simply reflect the United States’ exceptional power. If so, then realist theories—as the body of literature most focused on the role of power in international politics—would lead us to expect significant counterbalancing: although bandwagoning occasionally occurs, states are generally expected to balance against powerful actors focused on projecting power beyond their borders. Yet, while some states, at some times, have attempted to check the United States, the scope of this counterbalancing has, as our argument predicts, been strikingly inconsistent. Equally important, the lack of balancing does not seem to be explained by the narrow range of situations—primarily where states are revisionist actors looking to gain for themselves (Schweller Reference Schweller1994) or so weak that defeat is inevitable (Labs Reference Labs1992)—where one expects bandwagoning.

The Cold War, for example, certainly saw the Soviet Union balance against the United States. Yet, as Trachtenberg (Reference Trachtenberg1999) demonstrates, this behavior had important limits. Indeed, by the 1960s, Soviet leaders sought to keep the United States engaged in European security rather than see the United States leave the continent. Nor was this just a temporary aberration, as Soviet strategists contemplating the end of the Cold War desired a continued American presence in Europe to hedge against a possible German threat.Footnote ¹⁹ Western European states have exhibited parallel tendencies. Despite having the power potential by the mid-Cold War to challenge the United States, European counterbalancing was largely absent, as calls from the mid-1970s onward to bolster intra-European cooperation against the United States regularly faltered. As Timothy Sayle documents, states such as Britain, France, and West Germany preferred to bank on offshore American security guarantees rather than commit to trusting one another (or Russia) (Sayle Reference Sayle2019, ch. 7).

Asia witnessed similar trends. For example, post-Cold War East Asia initially saw both Japan and China bid to keep the United States engaged in the region despite concerns among analysts that one or both states might try to counter the United States (Christensen Reference Christensen1999). And, while it is true that China today is balancing the United States, it is worth noting the elements of consistency in Chinese strategy. Defense spending as a percentage of Chinese gross domestic product has remained steady; China has cultivated only a few weak allies; and much of Chinese military doctrine is geared more to defending against an American attack rather than pushing the United States out of East Asia (Fravel Reference Fravel2019; Shifrinson Reference Shifrinson2020a). In short, counterbalancing against the United States has been muted even on the part of capable actors—an outcome consistent with our logic.