This is a rich, impressive and timely book. At a time when American and neoliberal triumphalism deny the significance of any revolution later than 1776, and when almost no-one in the social sciences is still studying either revolution or class, Fred Halliday has demonstrated that we have been living in a revolutionary age, dominated by the conjoined effects of war and class revolution. In case you find his sub-title mysterious, Karl Marx noted that the Europe of his time was dominated by five Great Powers, but Revolution, ‘the sixth Great Power’, would soon overcome them all. Halliday would suggest that Marx was only half-right. Revolution did not overcome all five Powers, but it did transform them all—and their successors. Hannah Arendt and Martin Wight also emphasized that couplings of war and revolution have dominated much of modernity. But Halliday adds that these are not to be seen as ‘disruptions’ of International Relations, they are International Relations, since they have set the overall parameters of the modern international system. They did so, he says, in three distinct revolutionary phases from the sixteenth century to the present-day: sixteenth-seventeenth century religious wars/revolutions, late eighteenth and early nineteenth century Atlanticist wars/revolutions, and twentieth century wars/revolutions which became increasingly dominated by communism.