The other defining aspect of Turkey's foreign policy was the country's long-standing strategic alliance with the United States. The Truman Doctrine in 1947 enunciated American intentions to guarantee the security of Turkey and Greece during the Cold War, and resulted in large-scale U.S. military and economic support. In 1948 both countries were included in the Marshall Plan and the OEEC for rebuilding European economies. The common threat posed by the Soviet Union during the Cold War led to Turkey's membership of NATO in 1952, ensuring close bilateral relations with the US. Subsequently, Turkey benefited from the United States' political, economic and diplomatic support, including in key issues such as the country's bid to join the European Union. In the post–Cold War environment, Turkey's geostrategic importance shifted towards its proximity to the Middle East, the Caucasus and the Balkans.