The National Republican Greek League was founded on 9 September 1941 by a former army officer, Colonel Napoleon Zervas, a centrist who had been expelled from the army after the failed pro-Venizelist coup d'état of 1935, and two of his friends, Leonidas Spais and Ilias Stamatopoulos. Like many other resistance movements founded during that time, the political orientation of the National Republican Greek League was Republican, with a strong dislike towards the exiled king, George II, and featured some vague leftist-socialist tendencies. In the aftermath of the four-year right-wing Metaxas dictatorship, which was strongly supported by the king, the monarchy was almost universally rejected, while social ideals for "social fairness" became the vogue among the various resistance groups. The founding charter of EDES explicitly demanded the "establishment in Greece of a Republican regime, of Socialist form", the "revelation of the treason of former King George II and the gang of the so-called 4th of August Dictatorship", calling for a thorough cleansing of the state and Greek social and public life from anyone "who has not proven a National Republican socialist conscience through actions". The charter acknowledged the prominent exiled Venizelist general Nikolaos Plastiras as its nominal political head, but due to his exile in France they failed to take his consent beforehand. For the time being, no reference to armed opposition against the occupying forces was made in the text. On the same day, Komninos Pyromaglou, a friend and assistant of Plastiras, left Nice, where Plastiras resided, for Greece. He was authorize by the general to form, on his behalf, a republican organization with socialist content", and prepare to turn both "against the Occupier" and against a return of the monarchy. After his arrival in Athens on 23 September, Pyromaglou came into contact with Republican circles, and after contacting Zervas took EDES' command. In October, a five-member Executive Committee was founded, with Pyromaglou as Plastiras' representative as General Secretary and Zervas as a simple member. As the organization grew, it succeeded in establishing links with the British Headquarters in Cairo, with a view to receiving funds, weapons and guidance. Under British pressure which at the time strongly supported the Greek monarchy, Zervas was forced to send a statement of loyalty to King George II in March 1942. This marked a silent breach with the vitriolic anti-monarchist attacks of the past months, and marked EDES's slow slide towards a more pro-monarchist stance.
Like most similar groups, EDES was initially limited to Athens. Having the support of many prominent Venizelist and Republican military figures, EDES came into contact with EAM and tried to establish some form of cooperation. The negotiations failed over the demands of the Communists for a merger of EDES with EAM and their distrust of Zervas' pro-British attitudes. On 23 July 1942, after intense British pressure and more than a month after the official appearance of the military wing of EAM, the Greek People's Liberation Army, Zervas, accompanied by Pyromaglou and a handful of companions, set out for the Valtos Mountains in Aetolia-Acarnania, an area with long traditions of guerrilla warfare stretching back to the Ottoman period. From then and until the end of the Occupation, Epirus would be the primary area of operations of the EDES andartes. Supported by British parachute drops, EDES quickly gathered some 100 fighters. The first major operation of EDES was "Operation Harling", the destruction of the Gorgopotamos viaduct by a joint force of British SOE commandos, and EDES and ELAS forces. While the successful operation, one of the greatest sabotage acts in occupied Europe, greatly boosted the prestige of the nascent Resistance, it also caused a significant rift between EDES and ELAS: the British loudly proclaimed and lauded Zervas' role in the operation, while ignoring the contribution – numerically far greater – of the leftist ELAS forces. While the rift was healed by British mediation, it presaged the problems that would appear in the future.
The left wing Greek People's Liberation Army on various occasions accused its rival organizations, and particularly EDES, for collaboration with the occupation forces. However, this accusation was as yet unfounded, at least concerning EDES' guerilla branch. Moreover, during the armed conflicts between ELAS and EDES in Athens, a propaganda war was launched with ELAS accusing EDES of collaboration, mainly due to gaining plausibility from the explicit exemption of EDES from German propaganda attacks. EDES was accusing ELAS for soviet perspective and crimes against non-communists. On the other hand, Stylianos Gonatas, initially a political leader of EDES in Athens, won the peculiar enmity of the organization because he supported the collaborationist Security Battalions and encouraged young officers to join their ranks, which led to hostility of the EAM groups towards him. The 12th Army of Nazi Germany attempted for a short time to coopt the EDES forces, and to use them against the ELAS, but this attempt failed and in July 1944 the EDES launched new attacks.
These internal conflicts caused rivalry between resistance groups and eventually escalated into civil war. In October 1943, ELAS launched an attack on EDES. These attacks triggered a civil war that would last until February 1944. After that, a fragile truce was established, which lasted until December, two months after the Liberation. Then, while the ELAS of Athens attempted to overthrow the government, other units stormed the EDES positions in Epirus. The latter was defeated and the remaining forces were evacuated to Corfu. After the defeat of the ELAS in Athens, EDES forces returned to Epirus, where part of them got involved to the expulsion of the Cham Albanians.
