扩张与收缩：论美国外交的周期性

自1801年托马斯·杰斐逊总统上台以来，美国外交即呈现出“扩张——收缩——再扩张——再收缩……”的周期模式。从上一次扩张到下一次扩张或从上一次收缩到下一次收缩的平均时间约为45年左右。迄今为止，美国外交经历了四个半周期。美国经济的周期性波动、国际局势的变动、国内思潮的转换等因素是推动美国外交扩张与收缩的主要动力。当前美国外交开始步入第五个周期的收缩期，这将对世界和中国产生重大影响。

Expansion and Contraction:On the Periodicity of U.S. Diplomacy

Ever since President Thomas Jefferson took office in 1801,the U.S.diplomacy has witnessed an "expansion contraction——a further expansion——another contraction…" cycle mode.The average time span between the last expansion and the next expansion or the previous contraction and the next contraction is about 45 years.So far,U.S.diplomacy has gone through four and a half cycle.Such factors as cyclical fluctuations in the U.S.economics,the changes of international situation,and the conversions of domestic ideological trends are the main driving force of U.S.foreign expansion and contraction.Just now,U.S.diplomacy has begun to step into the contraction period of the fifth cycle,which will have a major impact on the world and China.