Turkey–United States relations refer to the bilateral relations between Turkey and the United States. Relations after World War II evolved from the Second Cairo Conference in December 1943 and Turkey's entrance into World War II on the side of the Allies in February 1945. Later that year, Turkey became a charter member of the United Nations. Difficulties faced by Greece after the war in quelling a communist rebellion, along with demands by the Soviet Union for military bases in the Turkish Straits, prompted the United States to declare the Truman Doctrine in 1947. The doctrine declared American intentions to guarantee the security of Turkey and Greece, and resulted in significant U.S. military and economic support. This support manifested in the establishment of a clandestine stay-behind army, denoted the "Counter-Guerrilla", under Operation Gladio. After participating with United Nations forces in the Korean War, Turkey joined the North Atlantic Treaty Organization in 1952.