Throughout four millennia of recorded history there has been no end to empire, but instead an endless succession of empires. After five centuries of sustained expansion, the half-dozen European powers that ruled half of humanity collapsed with stunning speed after World War II, creating a hundred emerging nations in Asia and Africa. Amid this imperial transition, the United States became the new global hegemon, dominating this world order with an array of power that closely resembled that of its European predecessors.Brazil, Russia, India, China, and the European Union now rise in global...