The Greek Civil War (Greek: E [], o Emflios [Plemos], "the Civil War") took place between 1943 to 1949. It was mainly fought against the established Kingdom of Greece (supported by the United Kingdom and the United States). The Kingdom won in the end. The losing opposition was governed by the Communist Party of Greece (KKE) and its military branch, the Democratic Army of Greece (DSE) and the People's Republic of the Provisional Democratic Government. The rebels were supported by Yugoslavia and the USSR. It began as a conflict between the communist-dominated left-wing resistance organization EAM-ELAS and loosely allied anti-communist resistance forces, and later escalated into a major Civil War between the Greek state and the communists. Fighting resulted in the defeat of the DSE by the Hellenic Army.The civil war resulted from a highly polarized struggle between left and right ideologies that started in 1943. From 1944 each side targeted the power vacuum resulting from the end of Axis occupation (19411944) during World War II. The struggle was the first proxy war of the Cold War and represents the first example of Cold War postwar involvement on the part of the Allies in the internal affairs of a foreign country, an implementation of Kennan's Containment policy in his Long telegram. Greece in the end was funded by the US (through the Truman Doctrine and the Marshall Plan) and joined NATO (1952), while the insurgents were demoralized by the bitter split between the Soviet Union's Joseph Stalin, who wanted to end the war and Yugoslavia's Josip Broz Tito, who wanted it to continue.The first signs of the civil war occurred in 1942 to 1944, during the Axis occupation of Greece. With the Greek government-in-exile unable to influence the situation at home, various resistance groups of differing political affiliations emerged, the dominant ones being the leftist National Liberation Front (EAM), and its military branch the Greek People's Liberation Army (ELAS) which was effectively controlled by the KKE. Starting in autumn 1943, friction between the EAM and the other resistance groups resulted in scattered clashes, which continued until spring 1944, when an agreement was reached forming a national unity government that included six EAM-affiliated ministers.

The immediate prelude to the civil war took place in Athens, on December 3, 1944, less than two months after the Germans had retreated from the area. After an order to disarm, leftists resigned from the government and called for resistance. A riot (the Dekemvriana) erupted; Greek government gendarmes opened fire on a pro-EAM rally, killing 28 demonstrators and injuring dozens. The rally had been organised under the pretext of demonstrating against the perceived impunity of the collaborators and the general disarmament ultimatum, signed by Ronald Scobie (the British commander in Greece). The battle lasted 33 days and resulted in the defeat of the EAM. The subsequent signing of the Treaty of Varkiza (12 February 1945) spelled the end of the left-wing organization's ascendancy: the ELAS was partly disarmed while the EAM soon after lost its multi-party character, to become dominated by the KKE.

The war erupted in 1946, when former ELAS partisans, who had found shelter in their hideouts and were controlled by the KKE, organized the DSE and its High Command headquarters. The KKE supported the endeavor, deciding that there was no alternative way to act against the internationally recognized government formed after the 1946 elections, which the KKE had boycotted. The Communists formed a provisional government in December 1947 and made the DSE the military branch of this government. The neighboring communist states of Albania, Yugoslavia and Bulgaria offered logistical support to this provisional government, especially to the forces operating in the north of Greece.

Despite some setbacks that the government forces suffered from 1946 to 1948, they eventually won, largely due to increased American aid, the failure of the DSE to attract sufficient recruits, and the side-effects of the TitoStalin split of 1948. The final victory of the western-allied government forces led to Greece's membership in NATO (1952) and helped to define the ideological balance of power in the Aegean Sea for the entire Cold War. The civil war also left Greece with a strongly anti-communist security arrangement, which would lead to the establishment of the Greek military junta of 19671974.

The Democratic Army of Greece (DAG; Greek: Δημοκρατικός Στρατός Ελλάδας - ΔΣΕ, romanized: Dimokratikós Stratós Elládas - DSE) was the army founded by the Communist Party of Greece during the Greek Civil War (1946–1949). At its height, it had a strength of around 50,000 men and women.

The DSE was backed up by the Popular Civil Guard (Λαϊκή Πολιτοφυλακή - ΛΠ), the Communist Party's security police force.