The parliamentary election of June 1915 gave Venizelos and the Liberals a majority of seats, but the king refused to recognize the result and withheld approval of the new government until August. In this critical period, Serbia's military position deteriorated, and Bulgaria used the opportunity to declare war on Serbia and reverse the Bulgarian losses of the Second Balkan War. In this process, Sofia also claimed Macedonia and Thessaloniki. Venizelos demanded that the army be mobilized according to the terms of the mutual defense treaty with Serbia. Constantine reluctantly agreed, but only if Greece itself were attacked. Then, without informing the king, Venizelos allowed the French and British to establish a northern front for their Gallipoli attack by landing troops in Macedonia. Before Constantine could react, Venizelos escalated tensions further by orchestrating a parliamentary declaration of war on Bulgaria, which also meant a declaration of war against the Central Powers. A war motion won by a thirty-seven-vote margin, heightening the conflict between Constantine and Venizelos.

Technically, the Greek constitution gave the monarch the right to dismiss a government unilaterally, but the general understanding was that the constitutional provision would only be used when the popular will of the nation was in doubt. Nevertheless, Constantine forced Venizelos to resign once again, dissolved the new parliament, and announced a new election for December 1915.