Talks between Western nations ended on April 4, 1949, when the foreign ministers of 12 countries in North America and Western Europe met in Washington, D.C, to sign the North Atlantic Treaty. It was primarily a security pact in which Article 5 stipulates that a military attack on one of the signatories would be considered an attack on all of them. When U.S. Secretary of State Dean Acheson (1893-1971) signed the document, it reflected a significant change in U.S. foreign policy. For the first time since the 1700s, the United States had formally linked its security to that of nations in Europe, the continent that had served as the focal point for the two world wars. Heavily influenced by the success of the Bolshevik revolution, American socialists and radicals gathered in Chicago in 1919 to create an American Communist Party. But the Americans were so divided that they instead created two parties. One group consisted mainly of relatively young Russian and Eastern European immigrants, who emphasized the attachment to Marxist orthodoxy and the proletarian revolution.
The other group, dominated by somewhat more pragmatic American radicals, sought mass influence. Such contradictory objectives, combined with the mismatch between communist doctrine and American reality, have made the communist movement in the United States a small denominational movement. After German reunification in 1990, the GDR withdrew from the pact. On 25 February 1991, at a meeting in Hungary, the pact was declared by the defence and foreign ministers of the six remaining member states. The USSR itself was dissolved in December 1991, although most of the former Soviet republics were the organization of the collective security treaty shortly thereafter. Over the next 20 years, the seven Warsaw Pact countries outside the USSR joined NATO (East Germany through reunification with West Germany and the Czech Republic and Slovakia as separate countries), as well as the Baltic states that were part of the Soviet Union. At the end of the 19th century, a new level of alliance building was reached in Europe, when hostility between Germany and France polarized Europe into two rival alliances.