COLIN POWELL REFERRED to the unfinished nature of the American promise when he declared that the question of America’s role in the world “isn’t answered yet.” The end of the Cold War, the rise of international terrorism, and the George W. Bush administration’s doctrines of preemption and unilateralism sparked new debates over the long-standing question of U.S. actions beyond its borders.

Americans had also debated for more than two centuries what responsibilities the government should shoulder and what was best left to private enterprise, families, churches, and other voluntary institutions. Far more than most industrialized democracies, the United States had relied on individual or private rather than collective or public solutions. In the twentieth century, Americans significantly enlarged the federal government’s powers, but since the 1960s fewer people trusted in government’s ability to improve people’s lives, even as a poverty rate of 20 percent among children continued and a growing gap between rich and poor intensified.

The see-sawing of control of the government between Republicans and Democrats from 1989 to 2010 reflected ongoing debate over government’s role in domestic affairs. The first Bush administration’s civil rights measure for people with disabilities and Bill Clinton’s incremental reforms both built on a tradition that sought to realize the American promise of justice and well-being. Those who mobilized against the ravages of globalization worked internationally for what earlier reformers had sought for the domestic population: protection of individual rights, curbs on capitalism and assistance for its victims, and fiscal policies that placed greater responsibility on those best able to pay. Even the second Bush administration, which sought to limit government’s reach, supported the No Child Left Behind Act, the Medicare prescription drug program, and a gigantic bail-out of failing businesses when the financial crisis hit the economy in 2008. The controversy over Obama’s efforts to stimulate the economy and to reform health care and the financial industry replayed America’s long-standing debate about the government’s appropriate role.

The United States became more embedded in the global economy as products, information, and people crossed borders with amazing speed and frequency. New waves of immigration altered the face of the American population. Globalization also contributed to the threat of deadly terrorism within America’s own borders. In response to those dangers, the second Bush administration launched wars in Afghanistan and Iraq. Obama ended the Iraq War in 2011, but he pursued terrorists aggressively and continued the war in Afghanistan. Both administrations sought to maintain U.S. preeminence in the world, but debate continued about how best to use that power.