The United States has about 800 military bases outside its borders and it is rarely noticed by policymakers. This permanent military presence abroad has significant costs and disadvantages. There are about 80,000 American troops in Europe and more than 150,000 in Asia, none of which protect their country from direct enemy attacks. It is as if United States plays the role of a global police force, but the question refers to the fact that how successful has it been, and to what extent has world violence been reduced?