The plan was to start the uprising in Moldavia and then move to Wallachia. The insurgents would combine their attacks with the pandur (guerrilla) militia led by the Wallachian revolutionary Tudor Vladimirescu, another veteran of the Tsar’s army in the Russo-Turkish war of 1806–12, whose peasant followers were in practice more opposed to their Phanariot rulers and landlords than they were to the distant Ottomans. The Treaty of Bucharest had placed the principalities under the joint sovereignty of Russia and the Ottoman Empire. They did not have any Turkish garrisons but the local hospodars were allowed to maintain small armies, which Ypsilantis expected to join the uprising as soon as his army of Greek volunteers from Russia crossed the River Pruth. Ypsilantis hoped that the revolt would spark a Russian intervention to defend the Greeks once the Turks took repressive measures against them. In the Moldavian capital of Ia
Without Russian support, the Greek uprising in the principalities was soon crushed by 30,000 Turkish troops. The Wallachian peasant army retreated to the mountains, and Ypsilantis fled to Transylvania, where he was arrested by the Austrian authorities. The Turks occupied Moldavia and Wallachia, and carried out reprisals against the Christian population there. Turkish soldiers looted churches, murdered priests, men, women and children and mutilated their bodies, cutting off their noses, ears and heads, while their officers looked on. Thousands of terrified civilians fled into neighbouring Bessarabia, presenting the Russian authorities with a massive refugee problem. The violence even spread to Constantinople, where the patriarch and several bishops were publicly hanged by a group of janizaries on Easter Sunday 1821.
As news spread of the atrocities, causing ever-stronger Russian sympathy for the Greek cause, the Tsar felt increasingly obliged to intervene, despite his commitment to the principles of the Holy Alliance. As Alexander saw it, the actions of the Turks had gone well beyond the legitimate defence of Ottoman sovereignty; they were in a religious war against the Greeks, whose religious rights the Russians had a duty to protect, according to their interpretation of the Treaty of Kuchuk Kainarji. The Tsar issued an ultimatum calling on the Turks to evacuate the principalities, restore the damaged churches, and acknowledge Russia’s treaty rights to protect the Sultan’s Orthodox subjects. This was the first time any of the powers had spoken out on behalf of the Greeks. The Turks responded by seizing Russian ships, confiscating their grain, and imprisoning their sailors in Constantinople.