The US-Japan alliance relation, one of the most significant two-side relation in the international relationship system, have been playing an important role in the international stage since the end of the World War Two.

Against the backdrop of bi-polar system in which socialist and capitalist blocs rivaled against each other, the development of Sino-Soviet and Franco-US alliances, which are alliances between superpower and regional power, shared a lot in common and had a wide range of differences.

Different from the existent summarizing papers on customs union,the author discusses the western viewpoints on the trade effect of customs unions from three logically connected aspects:first,the interest source of customs union;second,the reasons for the formation of customs union;and third,the determination of optimal external tariffs.

The Impact of EU s Eastern Enlargement on Trade Between China and the EU——Based on the Analysis of The Trade Effect of Customs Unions;