The administration of President George W. Bush has recognized that new security threats and new military capabilities require a new U.S. global defense posture. Nowhere are those changes more evident than Northeast Asia, and on the Korean Peninsula in particular. The redeployment of U.S. forces in South Korea has profound implications for Japan, its alliance with the United States and regional security.

Secretary of Defense Donald Rumsfeld took office with plans to reconfigure the U.S. military to better fit security realities of the 21st century. That task took on additional urgency in the aftermath of the 9/11 terrorist attacks as policymakers became acutely aware of the mismatch between military capabilities and security threats.

In Northeast Asia, the need for change seemed especially urgent: some 37,000 U.S. forces are tied down in a less than optimal deployment; the troops are exposed to a North Korean assault, and indeed serve as a "trip wire" to ensure a wider U.S. engagement in any North-South conflict. Many believe that South Korea should do more to shoulder the burden of its own defense. An even greater number are convinced that the trip-wire function is outdated: U.S. troops do not need to be held "hostage" to a North Korean attack to ensure a U.S. response. That argument became even more compelling as U.S. forces were needed in other theaters around the world.