The post–Cold War era began with a decade of conflicts often mediated by the United States as the world?s only remaining superpower. The September 11 terrorist attacks, however, marked the dawning of a new era. The United States became preoccupied by the wars in Afghanistan and Iraq, while around the world, new challenges and threats emerged: a more assertive Russia, an increasingly powerful China, dangerous terrorism organizations, and a refugee crisis in the Middle East that spilled into Europe.