Sweden was officially a neutral country and remained outside NATO and Warsaw Pact membership during the Cold War, but privately Sweden's leadership had strong ties with the United States and other western governments. Following the war, Sweden took advantage of an intact industrial base, social stability and its natural resources to expand its industry to supply the rebuilding of Europe. Sweden received aid under the Marshall Plan and participated in the OECD. During most of the post-war era, the country was governed by the Swedish Social Democratic Party largely in co-operation with trade unions and industry. The government actively pursued an internationally competitive manufacturing sector of primarily large corporations.