I review and critique three important recent books to clarify the ways in which empires amass territories, dominate the peoples within them, and sooner or later decline and disappear. I review definitions of empires and contrast empires with nation-states. Empires succeed to the extent to which they manage differences among subjects, and I examine explanations for empires’ varying strategies for accomplishing that necessary task. I examine how empires both suppress and inadvertently foster nationalism. Imperial dynamics were influenced by competition with rival empires even as empires learned from each other's successes and failures. Throughout the modern era ancient Rome was a model and a caution. I identify the ways in which wars led to imperial expansion and moments when wars weakened or fatally undermined empires. I contrast ancient and modern and European and Asian empires. Finally, I look at the nineteenth-century expansion and twentieth-century collapses of modern empires and speculate on the extent to which those trajectories hold lessons for the contemporary United States.