We extend the theoretical framework of an independent economy developed by Tao [Phys.Rev.E 82 (2010) 036118]so as to include multiple economies.Since the starting point of our framework is on the basis of the theory of the competitive markets of traditional economics,this framework shall be suitablefor any free market.Our study shows that integration of world economies can decrease trade friction among economic systems,but may also cause a global economic crisis whenever economy disequilibrium occurs in any one of these economic systems.