Robert Kagan’s latest book is a short but powerfully written argument about the return of great power conflict and the danger of believing that history is moving towards a world of liberal democracies living at peace with one another. The prospect of “a new era of international convergence” has faded. “History has returned,” he announces, and — however embattled the democracies may be — they “must come together to shape it, or others will shape it for them”.

Kagan somewhat overstates his case when he suggests that great power competition has been on the increase in recent years and that a 19th-century diplomat would instantly recognise the “elaborate dances and shifting partnerships” of today’s great power competition. Great power competition did not disappear with the end of the Soviet Union, but it is not clear that it is getting worse in recent years.

Kagan is most convincing — and this is ­really the central point of his book — when he points to the return of a kind of ideological conflict, this time in a form reminiscent of the 19th century, rather than the Cold War. “The rulers of Russia and China,” he writes, “like the rulers of autocracies in the past, do have a set of beliefs that guides them in both dom­estic and foreign policy.” Even though they have abandoned Marxist ideology, it would be a mistake to think that they had become mere pragmatists, pursuing selfish interests and believing in nothing. To the contrary, these autocratic rulers “believe in the virtues of a strong central government and disdain the weaknesses of the democratic system”.

Thanks to their substantial economic success — and, in the case of Russia, thanks also to the economic disaster in the 1990s — autocracy in both countries has acquired a kind of legitimacy. “It would be a mistake,” Kagan asserts, “to believe that autocracy has no international appeal.” But today’s autocrats lack the legitimacy conferred in the 19th century by the doctrine of “divine right”, and this, in a way, makes them more dangerous. “Today’s autocracies,” Kagan says, “struggle to create a new kind of legitimacy, and it is no easy task.” Integration into a world dominated by democratic ideology is thus threatening to them, and they will try to push back violently.