This was due to events which had a significant impact on the country's demographic structure, such as the First World War, the genocide of Greeks, Armenians and Syriacs (including: Arameans, Assyrians, and Chaldeans), and the population exchange between Greece and Turkey, and the emigration of Christians (such as Assyrians, Greeks, Armenians etc.) to foreign countries (mostly in Europe and the Americas) that actually began in the late 19th century and gained pace in the first quarter of the 20th century, especially during World War I. Today there are more than 200,000–320,000 people of different Christian denominations, representing roughly 0.3–0.4 percent of Turkey's population, including an estimated 80,000 Oriental Orthodox, 35,000 Catholics, 18,000 Antiochian Greeks, 5,000 Greek Orthodox, 8,000 Protestants, and 512 Mormons. There is also a small group of ethnic Orthodox-Christian Turks (mostly living in Istanbul or Izmir) who follow the Greek Orthodox or Syriac Orthodox church and additionally Protestant Turks who still face difficulties regarding social acceptance and also historic claims to churches or property in the country because they are from recent converts from Muslim Turkish backgrounds (rather than ethnic minorities). Ethnically Turkish Protestants number around 7,000–8,000. In 2009 there were 236 churches open for worship in Turkey. The Eastern Orthodox Church has been headquartered in Constantinople since the 4th century.