The establishment of this second Greek state had its origins in the debate over Greece's entry into the war on behalf of the Entente, as advocated by Venizelos, or a Germanophile neutrality as preferred by King Constantine I.

In 17 August 1916,[1] as parts of eastern Macedonia were not defended by the royal government against a Bulgarian invasion, Venizelist officers of the Hellenic Army launched an Entente-supported coup in Thessaloniki.

After a brief hesitation, Venizelos and his principal supporters joined the uprising and began the establishment of a second Greek government in the north of the country, which entered the war on the side of the Entente.

The National Defence government endured until 29 May 1917, when the Entente powers forced Constantine I to abdicate, and allowed Venizelos to return to Athens as Prime Minister of a unified country.

The status of the Greek-occupied eastern Aegean islands was left undetermined, and the Ottoman Empire continued to claim them, leading to a naval arms race and mass expulsions of ethnic Greeks from Anatolia.

At this point the first rifts appeared among the Greek leadership: Prime Minister Eleftherios Venizelos, at the helm since 1910 of a modernising government looking towards the British and French models, supported entry in the war on the side of the Entente, while King Constantine I, who had been educated in Germany, married to Kaiser Wilhelm II's sister and a deep admirer of Prussian militarism, anticipated a German victory.

Incensed by the successive humiliations and the Bulgarian advance in Macedonia, several Greek officers had flocked to Thessaloniki and volunteered to raise troops and join the Allies.

Colonel Epameinondas Zymvrakakis, about 600 men of the Cretan Gendarmerie with three volunteer companies under Major Neokosmos Grigoriadis and thirty other officers blockaded the headquarters of III Corps.

Sarrail arrived on the scene soon after, and commanded all Greek officers who would not join the newly formed "National Defence Committee" uprising to be shipped to southern Greece.

2 September], the "National Defence" received its first substantial reinforcement, as Colonel Nikolaos Christodoulou arrived in the city with the remnants of IV Corps that had refused to surrender and instead withdrawn via Kavala and Samothrace.

[3] Venizelos himself with his closest aides left Athens on 12/25 September, initially for his home island of Crete, and from there via Chios and Lesbos to Thessaloniki, where he arrived on 24 September/7 October.

The State of National Defence established control in Greek Macedonia, Crete and the northern Aegean islands; lands that were just recently liberated during the Balkan Wars.

Venizelos returned to Athens, as head of a superficially reunified Greece, and led it to victory alongside the Allies in World War I, but also in its entanglement in the subsequent Asia Minor Campaign.

But the revolution was also an expression of the wide rift between the quasi-Republican, progressive Venizelists and the conservative Royalists/Anti-Venizelists, and its outbreak marks also the beginning of the Greek National Schism which would leave a troublesome legacy to the country, as it continued in various forms up to the 1970s.

A popular song of the era celebrating the movement was performed by the musical Estudiantina of Smyrna named Tis aminis ta pedià (the lads of the Defence) or the Macedon.