SHANGHAI — U.S. Secretary of State Hillary Clinton this week has embarked on her first overseas trip to Asia as America's chief diplomat. While the leadership in all four capitals she visits are eager to gauge the pulse of the new U.S. government, Beijing is probably more anxious to figure out the Obama administration's thinking on China and its vision of U.S.-China relations, a subject that was substantively absent from the runup to last year's presidential election.

While it is still too early to enunciate the substance of Obama's China policy, it might be useful to predict the future of Sino-American relations in the context of historical patterns. One theory generalizes that U.S. foreign policy is characterized by alternative periods of introversion and extroversion, with each lasting about a quarter century.

The last "offensive" episode began in the 1980s with the Reagan administration. It featured the "second cold war" and climaxed with the Soviet collapse. One can argue that after some 25 years of expansion, U.S. foreign policy may enter another period of strategic contraction under the Obama administration.