The Soviet Union began to expand its sphere of influence after World War II and by 1948 had consolidated communist rule throughout Eastern Europe. In order to provide a system of collective security for European countries still outside the area of Soviet control, the North Atlantic Treaty was signed on 4 April 1949 by the United States, Canada, and 10 European countries.
Van Kappen, Franklin E.
"Military Issues in Nato: Dialogue or Monologue?,"
Naval War College Review: Vol. 42
, Article 7.
Available at: http://digital-commons.usnwc.edu/nwc-review/vol42/iss2/7