To this end, the U.S. government has expanded its sprawling Cold War-era network of security commitments and military bases. It has reinforced its existing alliances, adding new members to NATO and enhancing its security agreement with Japan. In the Persian Gulf, it has sought to protect the flow of oil with a full panoply of air, sea, and land forces, a goal that consumes at least 15 percent of the U.S. defense budget. Washington has put China on a watch list, ringing it in with a network of alliances, less formal relationships, and military bases.
The United States' activism has entailed a long list of ambitious foreign policy projects. Washington has tried to rescue failing states, intervening militarily in Somalia, Haiti, Bosnia, Kosovo, and Libya, variously attempting to defend human rights, suppress undesirable nationalist movements, and install democratic regimes. It has also tried to contain so-called rogue states that oppose the United States, such as Iran, Iraq under Saddam Hussein, North Korea, and, to a lesser degree, Syria. After 9/11, the struggle against al Qaeda and its allies dominated the agenda, but the George W. Bush administration defined this enterprise broadly and led the country into the painful wars in Afghanistan and Iraq. Although the United States has long sought to discourage the spread of nuclear weapons, the prospect of nuclear-armed terrorists has added urgency to this objective, leading to constant tension with Iran and North Korea.
In pursuit of this ambitious agenda, the United States has consistently spent hundreds of billions of dollars per year on its military -- far more than the sum of the defense budgets of its friends and far more than the sum of those of its potential adversaries. It has kept that military busy: U.S. troops have spent roughly twice as many months in combat after the Cold War as they did during it. Today, roughly 180,000 U.S. soldiers remain stationed on foreign soil, not counting the tens of thousands more who have rotated through the war zones in Afghanistan and Iraq. Thousands of American and allied soldiers have lost their lives, not to mention the countless civilians caught in the crossfire.