Jane Burbank and Frederick Cooper are history professors at New York University, and the authors of Empires in World History: Power and the Politics of Difference, Princeton University Press, 2010.

Why, in 2011, think about empires? We live in a world of nation-states — over 200 of them, each with their seat in the UN, their flag, postage stamps and governmental institutions. Yet the nation-state is an ideal of recent origin and uncertain future and, for many, devastating consequences.

Empire did not give way to a secure world of nations with the end of Ottoman, Austro-Hungarian, Romanov or German rule after the first world war or, in the 1940s-1970s, with decolonisation (by the French, British, Dutch, Belgian and Portuguese). Many recent conflicts — Rwanda, Iraq, Israel, Afghanistan, ex-Yugoslavia, Sri Lanka, the Congo, the Caucasus, Libya, etc — emerged from failures to find viable alternatives to imperial regimes, after 1918, 1945 and 1989.

It is not a question of sinking into imperial nostalgia: sentimental evocations of the British Raj or French Indochina have nothing to offer to our present political thinking. Similarly, imperial name-calling — invoking "empire" or "colonialism" to discredit US, French or other interventions — cannot help us analyse or improve today’s world. But an exploration of the histories of empires, old and new, can expand our understanding of how the world came to be what it is, and the organisation of political power in the past, the present and even the future.

Over a very long time, the practices and interactions of empires configured the contexts in which people acted and thought. Examining the trajectories of empires — their creations, conflicts, rivalries, successes and failures — reminds us of something we have forgotten: that sovereignty in the past, and in many areas today, is complex, divided, layered and configured on a variety of founding principles and practices.

What gave empires their world-shaping force?..