In Untied Kingdom, Stuart Ward, a professor of history at Copenhagen, and of Australian extraction, retells the story of the decolonisation of the British Empire against the to-be-determined question of whether the UK itself will unwind. His is a well-told narrative of related endings.

One is the end of the idea of Greater Britain, first propagated by Charles Dilke in the late nineteenth century, and romanticised more recently in erudite word-clouds by New Zealander J. G. A. Pocock, a doyen of the history of early modern political thought.

Another is the end of the British Commonwealth of Nations, originally an imperial confederation into which many sought to restructure the ‘white dominions’ – with significant sentimental success in British Canada and the British Antipodes. Acceptance was much less evident in South Africa, despite being championed by Jan Christian Smuts. Over time, neither the racially excluded non-whites, nor the Boers, the other white settler community, found ‘Britishness’ to their liking. The British identity was insufficiently democratic or liberal for the former, and too liberal and insufficiently racist for the latter.

Unobserved by Ward, in 1921 Ireland was forced to accept Commonwealth membership as a means to oblige it to recognise ‘the Crown’, and in hopes of controlling its foreign and defence policy. Article 1 of the 1921 treaty provided that ‘Ireland shall have the same constitutional status in the Community of Nations known as the British Empire as the Dominion of Canada, the Commonwealth of Australia, the Dominion of New Zealand, and the Union of South Africa.’ Article 2 specified that ‘the law, practice and constitutional usage’ related to Canada would apply to the Irish Free State. The latter clause would be skilfully exploited by the new state to establish its sovereignty more quickly than Lloyd George and Conservatives had hoped.

The exit of the Irish Free State from the UK is not one of Ward's major case studies of British endings – admittedly these were so numerous in the twentieth century that he may be entirely excused, but it was the first, and it was accompanied by an unjust partition, and that became a precedent for British withdrawals from India and Palestine.

At independence, India, further away than Ireland and benefiting after 1945 from British weakness and Soviet and US promotion of self-determination, could not be coerced into any British definition. There were just not enough Britons. The fitful transition to ‘the Commonwealth’ took place at Nehru's insistence. ‘Bitter-ender’ resistance to the change of name came from those ‘more British than the British themselves’, the Australians and the New Zealanders. India also became a member as a republic, a right that had been denied to Ireland.

Another end to Greater Britain occurred through the punctuated withdrawal of the UK from the Commonwealth as a market for goods (‘imperial preference’) and as a zone of freedom of movement.

Bidding to join the European Economic Community in 1961, the UK abandoned its obligations to the Commonwealth, a task not completed until 1973. The ‘imperial subject’ was also downsized as British citizenship was incrementally defined and confined – through tacit rather than explicit racism. Citizenship was confined to those from Great Britain and Northern Ireland, and their immediate descendants, with special franchise and movement arrangements for the white Commonwealth and the Irish-born.

Ward elegantly relates other endings, notably the slow replacement of British symbols – flag, emblem, anthem – in the white commonwealth and the Caribbean, matched by faster-paced transitions where British settlers had been less numerous or powerful. ‘Cosmologies of our own’ accompanied the formation of many new nation states.

Ward does not register all retentions: British ‘sovereign bases’ in Cyprus now have their own Protocol in the UK's withdrawal from the European Union. Also missing is a sustained treatment of the insurgencies that speeded the termination of the British Empire: in Ireland, Iraq, India, Kenya, Cyprus, Malaya, Aden and elsewhere. He is fully aware of them, and of the atrocities generated. The Mau Mau insurgency is noted, and its brutal suppression; equally commendably he emphasises the often-forgotten destruction rained on Egyptians in the invasion of the Suez Canal by the UK, France and Israel.

Ward knows the facts and the historiography but does not draw on Caroline Elkins's parallel panorama, Legacy of Violence: A History of the British Empire (it is in his bibliography), or her earlier work with Susan Pedersen on Settler Colonialism in the Twentieth Century. Charles Townshend's Britain's Civil Wars: Counterinsurgency in the Twentieth Century is also overlooked; generally impartial and accurate, it displays too much sympathy with the British counter-insurgents for my taste.

Crudely summarising, the British fought to keep their empire where they could, especially where they had strategic interests (albeit subject to constant redefinition). Elsewhere, they were relatively fast-paced downsizers when the costs of retention were judged too high. John Seeley's significantly titled The Expansion of England (1883) infamously suggested that ‘We seem, as it were, to have conquered and peopled half the world in a fit of absence of mind.’ In fact, there was as much mindfulness and ruthlessness in winding up much of the empire as there had been in its construction, and Ward fully recognises that.

The book's style is literary. Most chapters are started with telling vignettes, rescuing episodes from obscurity: for example, sailing Sikhs refused admission to Canada by British Columbian officials and courts in 1914, and a governor of Kenya permanently gifting a hunting lodge to Princess Elizabeth to encourage future royal visits. The Fleming brothers (one the inventor of James Bond) are deployed to open a discussion of receding frontiers after the withdrawal from Suez under American orders, while the brutal hanging of three founding members of the Zimbabwe African National Union (ZANU) by Ian Smith's Rhodesia, just before its unilateral declaration of independence, opens an account of the failure of British justice.

The author is also a British-style historian; that is to say, he reads other historians and evidently does not read social scientists much. No data are presented in tables; surveys are reported in sentences; the figures are photographs. Conceptual precision and clear theory-testing are avoided, and his methodology is sometimes as loose as the empire under scrutiny. All that is especially evident in his treatment of Northern Ireland. He ‘sidesteps’ the ‘conceptual logjam’ over whether Ireland ought to be considered a [past] colony. There is no such logjam, just a clear difference between those willing to define, operationalise, and test against evidence, and those who fear that lurking beneath any notion of colonialism is a notion of decolonisation that they find unwelcome.

Ward wants to argue that the decline of Greater Britain has impacted the core: the United Kingdom of Great Britain and Northern Ireland. That is plausible, but he cannot sidestep the colonial question. Ulster unionists feared that the withdrawal of British support from white settlers – in Kenya and Rhodesia – and sudden British withdrawals (‘scuttles’) from India and the Middle East set terrifying precedents.

True, but they had these fears because they knew their own standing derived from past settler colonialism, of which they were palpably proud (and from a biased partition, for which the Conservatives were largely responsible), and because they knew that most of the downsizing British of Great Britain had little sympathy for them. To many of the British of Great Britain, the Ulster British were, and sometimes remain, embarrassing reminders of what their ancestors had been like.

Many Irish nationalists and republicans also took comfort from the evident weakening of the British Empire, seeing the same precedents in similar light. Neither unionists nor nationalists were fools.

And the British army sent in 1969 to keep the peace between them soon behaved as it had done in Aden, Cyprus, Kenya and Malaya, guided by counter-insurgency strategy and tactics taught at Sandhurst – and that too helps explain the ‘explosiveness’ (Ward's word) of ‘the Troubles’. Here it is evident that Ward is too reliant on some recent historians of Ireland who collectively share more hostility to Irish republicanism than to British imperialism – and the British army.

The rest of this decade is set to be an interregnum in which the twilight of the Union of Great Britain and Northern Ireland will be visible, but the new cannot yet be born. In these years Ward's book should be read both by those who wish to preserve the Union of Great Britain and Northern Ireland, and those who would like to see Irish reunification.

Untied Kingdom will remind readers that there have been several disastrous exits from past British commitments: Brexit is just one sample. Sovereign Ireland can certainly afford Northern Ireland, but its government must plan for the contingent possibility of an irresponsible British withdrawal, as well as prepare to make a success of reunification through the referendums provided for in the Good Friday Agreement.