In this century, the world will conduct an extraordinary experiment in government. In 2050, forty percent of the planet's population will live in just four places: India, China, the European Union, and the United States. These are superstates - polities that are distinguished from normal countries by expansiveness, population, diversity, and complexity.

How should superstates be governed? What must their leaders do to hold these immense polities together in the face of extraordinary strains and shocks? Alasdair Roberts looks to history for answers. Superstates, he contends, wrestle with the same problems of leadership, control, and purpose that plagued empires for centuries. But they also bear heavier burdens than empires - including the obligation to improve life for ordinary people and respect human rights.

One axiom of history was that empires always died. Size and complexity led to fragility, and imperial rulers improvised constantly to put off the day of reckoning. Leaders of superstates are doing the same today, pursuing radically different strategies for governing at scale that have profound implications for democracy and human rights. History shows that there are ways to govern these sprawling and diverse polities well. But this requires a different way of thinking about the art and methods of statecraft.