The NATO’s eastward expansion is an important factoraffecting Russia-U.S. relationship and European future security configuration.The changes in political and security borders of Europe caused by the NATO’s eastward expansion, the deployment of anti-ballistic missile systems in Europe, together with the conventional military forces recently deployed, are bound to arouse heated controversies. Although at the 2017 NATO Summit in Munich, the United States reiterated its support for alliance with the NATO, which illustrates the U.S. has already begun to gradually get rid of the “presidential election effects”. The U.S. has returned to maintaining its traditional position of relations with the North Atlantic allies. Nevertheless, it’s yet to be observed whether today’s NATO’s expansion will repeat mistakes of the past, that is, beginning with pursuing monism but finally ending with co-existence of multiple powers.