King Constantine of Greece, himself from a Germanic background and married to a sister of Kaiser Wilhelm II, was believed by the British and their Allies to be a pro-German who wished to make Greece an ally of the Central Powers. Public anti-war sentiment and the presence of Allied warships forced him to remain neutral, but the British always viewed him as an enemy.

Prime Minister Venizelos deeply wanted the Greeks to side with the Allies in World War I. On his own initiative, he invited the British and French to occupy Thessaloniki as a spearhead in their fight against the Bulgarians and Ottomans. The king prorogued parliament, forcing Venizelos from power.

In 1916, supporters of Venizelos staged a revolt, and Venizelos became the prime minister of a revolutionary government in Thessaloniki. A civil war ensued between Royalists supporting King Constantine and Venizelists. The Allies, confident that Venizelos would join their side in the war, recognised the revolutionaries as the government of Greece. They instituted a blockade of more than three months of Royalist-controlled regions of Greece to force the Royalists to resign power. The French occupied Thessaly and threatened to bombard Athens if Constantine did not abdicate. In June of 1917 he left Greece, but never formally abdicated. His second son, Alexander, became king, reigning as the puppet of Venizelos and the Allies. Venizelos became prime minister of all Greece. He brought Greece into the war on the side of the Allies.

Greece remained deeply divided. King Constantine retained much support. While Venizelos was the image of Greece for the Allies, he was not nearly as popular in war-weary Greece. Much of Greece opposed the entry into the world war and the subsequent Greek occupation in Anatolia. King Alexander died on 26 October 1920. Venizelos's Liberal Party lost the election of 1 November 1920 to the People's Party of Dimitrios Gounaris. Dimitrios Rallis became prime minister on 17 November 1920, replaced in two months by Nikolaos Kalogeropoulos, who lasted for three months. Gounaris became prime minister on 8 April 1921. A plebiscite on 22 November 1920 returned Constantine as king by an overwhelming majority, to the consternation of the Allied Powers. He retook the throne on 19 December.