What caused the Armenian Genocide in the Ottoman Empire?
First of all, please understand that this is a very controversial topic. Turkey denies vehemently that this was a genocide.
The main reason for the deaths of the Armenians is the fact that they were ethnically and religiously different from the majority of the population of the Ottoman Empire (which was ruled by the Turks).
Because of this, they made ideal scapegoats during World War I. In WWI, the Ottoman Empire was defeated by the Allied Powers. During the war, the Armenians were suspected of helping the Allied Powers, especially the Russians. For this reason, they were targeted.
In many ways, the extreme chaos and upheaval caused in the world after the First World War helped to permit the slaughter of the Armenians. The harsh terms caused by the Treaty of Versailles, as well as huge loss of life on both sides, and the Russian Revolution literally cast Europe in a complete sense of disarray. This allowed the perfect cloak for the Turks to consolidate power by eliminating the Armenians. Indeed, the Turkish authorities deny that this happened and will not accept responsibility for it. However, it is difficult to accept this response.