In the aftermath of the Cold War, many scholars predicted that American alliance system would collapse. However, as the only one of hegemony in the Post-Cold War era, the U.S. continued to adopt the strategy of alliances and pay much attention to the allies in its national strategy. This article concludes some main concerns from the U.S. side. The first is to maintain America's primacy and bind its allies. The second is to cope with the complex situations in the global politics. The third is that democracies tend to develop good cooperation and make alliances with each other. The last is to shape the legitimacy and legality of its international operations. Even facing the rise of other powers, the U.S. still maintains its alliance system of hegemonic leadership. The strategy can prevent the U.S. itself from being controlled and keep its dominance.