When a state adopts a strategy to increase employment or to prevent pollution on its own territory, it has no rivals. Of course, certain citizens, employers, trade unions or pressure groups may have other ideas and try to thwart the government's plans. But there is no other state or entity with the legal authority to adopt an alternative strategy for the same issues on the same territory. In domestic politics, every state reigns supreme. If another state does try to interfere, that constitutes an act of subversion, which will likely result in retaliation.

International politics, in contrast, is inherently competitive: states operate alongside each other in the same geographic theatres, international organisations and thematic policy areas, each pursuing its interests through its own grand strategy. The competitive nature of grand strategy is probably its most obvious characteristic, and yet it is often forgotten that the other players have a strategy too, or they are underestimated. ‘Always remember, however sure you are that you can easily win, that there would not be a war if the other man did not think he also had a chance’: Churchill's quote applies just as much to peacetime grand strategy. Great powers and other states alike, when designing strategy, must take into account not only the limitations imposed by their own resources and the constraints of the environment, but also the fact that other players will be pursuing a proactive grand strategy of their own. As General Montgomery, frustrated with the state of planning, wrote to General Alexander prior to the allied landing in Sicily in 1943: ‘I have been ordered to invade the mainland of the continent of Europe on the 30th August. In the absence of information to the contrary, I must assume that some resistance will be offered by the enemy.’

States cannot be but competitors, as they seek influence, partners, markets and resources in the same countries and organisations. Such competition is natural; economic competition, moreover, is inherent to capitalism. Normal competition can turn into rivalry, however, if one state perceives foul play by another. A state that does not apply reciprocity, bending or evading the rules that other states observe, or that seeks to fence off markets and resources for its own exclusive use, may provoke the active rivalry of its competitors.