Among all the tragedies and schisms which thinned the Church out, no other was as severe as the Assyrian genocide. At that point the Assyrian Church of the East was based in the mountains of Hakkari, as it had been since 1681. In 1915, The Young Turks invaded the region — despite the Assyrians' plea of neutrality during the Caucasus Campaign by Russia and their Armenian allies — out of fear of an Assyrian independence movement. In response to this, Assyrians of all denominations (the Assyrian Church of the East, the Chaldean Catholic Church, the Syriac Orthodox Church and Assyrian Protestants) entered into a war of independence and allied themselves with the United Kingdom, the Russian Empire and the Armenians against the Ottomans and their Islamic Kurdish, Iranian and Arab allies. Despite the odds, the Assyrians fought successfully against the Ottomans and their allies for three years throughout southeastern Turkey, northern Iraq, northwestern Iran and northeastern Syria. Eventually, however, they were abandoned by their allies, the Russian Empire and the First Republic of Armenia, due to the Russian Revolution and the collapse of the Armenian defense, leaving the Assyrians vastly outnumbered, surrounded, and cut off from supplies of ammunition and food. During this period, their see at Qodchanis was completely destroyed and the Turks and their Islamic allies massacred all of the Assyrians in the Hakkari Mountains. Those who survived fled into Iran with what remained of the Assyrian defense under Agha Petros, but they were pursued into Iranian territory despite the fact they were fleeing. Later, in 1918, after the murder of their "de facto" leader and patriarch Shimun XIX Benyamin and 150 of his followers during a negotiation, fearing further massacres at the hands of the Turks and Kurds, most of the survivors fled by train from Iran into what was to become Iraq. They sought protection under the British mandate there, and joined the already existing indigenous Assyrian communities of both Eastern Orthodox and Catholic rites in the north, where they formed communities in Baghdad, Basra, and other areas.