Back in 1942, Britain and the USSR mobilized troops into Iran to safeguard its oil supplies from Italy and Germany. These tropps were supposed to be removed after six months. However, the Soviets increased their troops, This was seen as athreat for Turkey and Iraq as well. The US had to appeal to the Security Council of the United Nations, and these troops were withdrawn succesfully.
Another attempt of Soviet expansion..
On 12March, Truman appealed to the Congress and outlined plan for financially assisting states like Greece and Turkey, which were perceived to be threatened by communism. Truman argued that the United States could no longer stand by and allow the forcible expansion of Soviet totalitarianism into free, independent nations, because American national security now depended upon more than just the physical security of American territory.
"The Truman doctrine"
It is the policy of the United States to support free peoples who are resisting attempted subjugation by armed minorities or by outside pressures.