Anatolia remained multi-ethnic until the early 20th century (see the rise of nationalism under the Ottoman Empire). During World War I, the Armenian Genocide, the Greek genocide (especially in Pontus), and the Assyrian genocide almost entirely removed the ancient indigenous communities of Armenian, Greek, and Assyrian populations in Anatolia and surrounding regions. Following the Greco-Turkish War of 1919–1922, most remaining ethnic Anatolian Greeks were forced out during the 1923 population exchange between Greece and Turkey. Of the remainder, most have left Turkey since then, leaving fewer than 5,000 Greeks in Anatolia today.