Perhaps the most momentous but least widely understood development in modern history is the long transition from a world of empires to a world of states. Until at least the late nineteenth century, and in many places for decades after, most of the world’s population lived in the territorially expansive, internally diverse, hierarchically organised political communities called empires. It is a striking feature of our political world that humanity is now divided into so many states but it is equally significant that there are no longer any self-styled empires. Although many commentators argued that the United States acted like an empire during the presidency of George W. Bush, ‘empire’ was not a name formally adopted or publicly promoted by even the most committed proponents of an aggressive American foreign policy after 2001. Indeed, the last soi-disant empire died in 1979 when French forces overthrew Jean-Bédel Bokassa, the Napoleonic emperor of the Central African Empire, now the Central African Republic.

In order to understand this great transformation of a world of empires into our world of states, it is essential to go back to the late eighteenth and early nineteenth centuries. This was a period in which empires competed aggressively and expanded successfully, from China under the Qing dynasty to Great Britain under the Hanoverian monarchy. But it was also a century in which other empires were under challenge, from the Mughals in South Asia to the Bourbons and Habsburgs in Europe and the Atlantic world. The number of polities we might recognise to be sovereign states was relatively small and many of them, especially in Europe, sought the greater prestige and resources that came with being, or having, an empire and ruling over diverse and far-flung peoples. It would be anachronistic to see the origins of a world defined by states as early as 1648 and the Peace of Westphalia which is often held to have inaugurated a ‘Westphalian order’ of mutually acknowledged independent states; it might even be anachronistic to find the roots of a state-based international order even 200 years later in the mid nineteenth century when empires were still on the rise and on the march across the world from Mexico to Russia in the late nineteenth century.