On the other hand, the rearmament of West Germany and its admission to the alliance were the apparent causes of the establishment of the Warsaw Pact in 1955.

In the early 1990s, the political transformation of the USSR and Eastern Europe, including the absorption of East Germany into the Federal Republic of Germany (West Germany) and the dissolution of the Warsaw Pact, drastically reduced the military threat to NATO. Nevertheless, many Western observers see NATO in the post-Cold War era as an umbrella of security in a Europe buffeted by the nationalist passions unleashed in Eastern Europe and the former USSR. The North Atlantic Cooperation Council, established in November, 1991, provides a forum for consultations between NATO members, East European nations, and the former Soviet republics. In 1993 NATO members endorsed a proposal to offer former Warsaw Pact members limited associations with NATO. Under the plan, known as Partnership for Peace, non-members could be invited to participate in information sharing, joint exercises, and peacekeeping operations. In May 1997 the leaders of Russia and the 16 countries in NATO signed an agreement intended to improve their relations and ease NATO's eastward expansion.