The Greek Civil War was fought from 1944 to 1949 between a government backed by British and American support and Greek Communists. American intervention resulted in the Truman Doctrine, the U.S. policy of aiding nations defending themselves against Communist forces.
During German occupation of Greece, much of the resistance consisted of the Communist National Liberation Front (EAM) and its military, the People's National Army of Liberation (ELAS). The Germans left Greece in September 1944 and Great Britain brought the former government of Greece, along with the now included EAM, back into power. Some of those in the ELAS, however, would not cooperate with the British-supported government and threatened to take control of Greece. When Great Britain suggested disarming the ELAS, a proposal that Communists were against, a general strike in Athens was declared by Communists on December 2, 1944. The next day, police and the ELAS came into conflict with each other. After Winston Churchill visited, a truce was signed and ELAS guerrillas withdrew from Athens. An agreement was reached on February 12, 1945 which called for the the ELAS to turn in its weapons within fourteen days.
However, the fight continued for two reasons. The Greek government was unstable and Greece also had territorial conflicts with Yugoslavia and Albania. Josip Broz Tito, the leader of Communist Yugoslavia, gave his support to the EAM-ELAS. The Communist forces of Greece retreated north into the mountains where they could be supported by the neighboring countries of Yugoslavia and Albania.
Britain sent 40,000 troops to Greece and gave financial aid to the government, which became dependent on Great Britain's military and financial assistance to stay in power. Unfortunately, Great Britain possessed its own financial difficulties and would not continue its support after March 31, 1947, the day of Greek elections.
On February 21, 1947, the United States was requested by Great Britain to give support to Greece and Turkey. President Truman asked Congress for $400 million of aid to Greece and Turkey.
In response, the ELAS announced the formation of a Communist government, the "Free Greek Government." With about 20,000 to 30,000 guerrillas, the ELAS fought its way south, nearly to Athens.
But U.S. financial aid stabilized the Greek government and its military assistance helped force the ELAS back to the north. Furthermore, a Communist party split ended Yugoslavian support. Yugoslavia disagreed with the Soviet Union on certain issues, dividing Communists into supporters of Tito and supporters of Stalin. The Greek Communist Party came to support Stalin and subsequently, Yugoslavia ended its support of the Greek rebels in July 1948.
The last significant refuge of the Greek Communists was captured on August 28, 1949. On October 16, ELAS announced its surrender.