International relations and conflicts, including the origins of the Cold War, can seldom be reduced to "a couple of details." There were many factors involved in development of the situation that came to be called the Cold War.
After the end of World War II, the Soviet Union was concerned about encroachment upon its territorial boundaries and about unfriendly influences on its neighboring countries, which were its primary allies and trade partners. The United States was suspicious of Soviet plans to expand the communist philosophy of government and economic planning and supported European allies in rebuilding democratic and free-capital economies. The conflict between these basic outlooks formed the beginning point for the Cold War, which
dominated the two powers' foreign policies, domestic priorities, and military planning for roughly the next forty-six years, having an impact on practically every nation on Earth.
The Cold War began in 1945 due to political differences between Russia and other countries including the United States. The United States as well as other countries formed NATO in 1949 as a result of these differences. Look here for more information: http://en.wikipedia.org/wiki/The_cold_wa...