The National Liberation Front (Greek: , Ethnik Apeleftherotik Mtopo (EAM)) was the main movement of the Greek Resistance during the Axis occupation of Greece. Its main driving force was the Communist Party of Greece (KKE), but its membership throughout the occupation included several other leftist and republican groups. became the first true mass social movement in modern Greek history. Its military wing, the Greek People's Liberation Army (ELAS), quickly grew into the largest armed guerrilla force in the country, and the only one with nation-wide presence. At the same time, from late 1943 onwards, the political enmity between and rival resistance groups from the centre and right evolved into a virtual civil war, while its relationship with the British and the British-backed Greek government in exile was characterized by mutual mistrust, leading EAM to establish its own government, the Political Committee of National Liberation, in the areas it had liberated in spring 1944. Tensions were resolved provisionally in the Lebanon Conference in May 1944, when EAM agreed to enter the Greek government in exile under Georgios Papandreou. The organisation reached its peak after liberation in late 1944, when it controlled most of the country, before suffering a catastrophic military defeat against the British and the government forces in the Dekemvriana clashes. This marked the beginning of its gradual decline, the disarmament of ELAS, and the open persecution of its members during the "White Terror", leading eventually to the outbreak of the Greek Civil War.

The Greek Civil War (Greek: ο Eμφύλιος [Πόλεμος], o Emfýlios [Pólemos], "the Civil War") was a civil war that took place between 1943 to 1949 in Greece, mainly fought between the Monarchist Kingdom of Greece (supported by the United Kingdom and the United States) and the People's Republic of the Provisional Democratic Government (Supported by Stalin's Soviet Union and the Eastern Bloc), governed by the Communist Party of Greece and its military branch, the Democratic Army of Greece (DSE). 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 (1941–1944) during World War II. The struggle was the first proxy war of the Cold War (c. 1947 to 1989) 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 (despite this intention however, Stalin still sent aid to the Greek communists), 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 German occupation. 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.Pritchard, Stephen (28 March 2015). "The readers' editor on … Athens, 1944". The Guardian. Retrieved 25 March 2022. 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 Tito–Stalin 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 1967–1974.