The 1st genocide of the 20th century was the Armenian Genocide. The Islamic Ottoman government systematically exterminated its minority Armenian (who were predominately Christians) subjects from their historic homeland in the territory constituting the present-day Republic of Turkey. It took place during and after WWI (1915-1923) and was implemented in 2 phases: the wholesale killing of the able-bodied male population through massacre and forced labor, and the deportation of women, children, the elderly and infirm on death marches to the Syrian Desert. The total number of people killed as a result has been estimated at between 1 and 1.5 million. The Assyrians, the Greeks and other minority groups were similarly targeted for extermination by the Ottoman government, and their treatment is considered by many historians to be part of the same genocidal policy. To this day, Turkey denies the genocide ever happened.
In the 1970s, the ASALA (Armenian Secret Army for the Liberation of Arnenia) was very active in the Armenian SSR and throughout Europe, and especially in Turkey. They targeted Turkish diplomats and citizens abroad. They killed a lot of people in their terrorism campaign.