For a century, the United States has been a global power, but it is still deeply ambivalent about its relationship with the rest of the world. Its assertive side was most vivid in the rebuilding years after World War II. If the world has benefited from its leadership and engagement, the United States itself has not done badly either.

Even so, echoes of Thomas Jefferson's warning against "entangling alliances" still resonate two centuries later. At different times in its history, the United States has declared semi- independence from the rest of the globe, imposing protective tariffs or refusing membership to international organizations like the League of Nations—with disastrous results for both itself and the world.

This tension between nationalism and internationalism exists on both sides of the political divide. Americanliberals tend to be more internationalistic; they champion international arms and environmental agreements alongside sustaining the International Monetary Fund (IMF) and the United Nations (UN), even if they have doubts about those institutions' operations. But even liberals reflect American suspicion of foreigners when it comes to trade. The American left shares with the right the belief that in trade the United States should look first to its own armory of measures rather than to collective agreement seeking mutual benefit.

For American conservatives, this nativism is their first instinct. A distrust of foreigners and assertion of U.S. interests unilaterally helps to define their patriotism. They believe the defense of U.S. institutions is the prime responsibility of the political class. They were never comfortable with the New Deal or the U.S.