In the aftermath of the First World War, Greece attempted further expansion into Asia Minor, a region with a large native Greek population at the time, but was defeated in the Greco-Turkish War of 1919–1922, contributing to a massive flight of Asia Minor Greeks. These events overlapped, with both happening during the Greek genocide (1914-1922), a period during which, according to various sources, Ottoman and Turkish officials contributed to the death of several hundred thousand Asia Minor Greeks. The resultant Greek exodus from Asia Minor was made permanent, and expanded, in an official Population exchange between Greece and Turkey. The exchange was part of the terms of the Treaty of Lausanne which ended the war.