Since World War II, despite the costly flare-ups in Korea and Vietnam, the United States has proved to be the essential guarantor of stability in the Asian-Pacific region, even as the power cycle shifted from Japan to the Soviet Union and most recently to China. The benefits of our involvement are one of the great success stories of American and Asian history, providing the so-called second tier countries in the region the opportunity to grow economically and to mature politically.

As the region has...