Christianity by country
According to Christian Today, there were 2.4 billion Christians around the world in 2015. And according to a 2012 Pew Research Center survey, if current trends continue, Christianity will remain the world's largest religion by year 2050. By 2050, the Christian population is expected to exceed 3 billion. Many charismatic movements are growing in Africa, Latin America, Muslim world, and Asia.Other religions:
Christianity in Turkey
Christianity in Turkey has had a long history dating back to the 1st-century AD. In modern times the percentage of Christians in Turkey has declined from 20-25 percent in 1914 to 3-5.5 percent in 1927, to 0.2% today. 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 Syriacs, Assyrian, Greeks, Armenians, and Chaldeans 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 people of different Christian denominations, represent less than 0.2 percent of Turkey's population, including an estimated 80,000 Oriental Orthodox, 35,000 Catholics, 18,000 Antiochian Greeks, 5,000 Greek Orthodox and 8,000 Protestants. There are also a small group of Protestant Turks whom still faces difficulties even though they are from recent Muslim Turkish backgrounds(rather than ethnic minorities)that don't have historic claims to churches or property in the country. Currently there are 236 churches open for worship in Turkey. The Eastern Orthodox Church has been headquartered in Constantinople since the 4th century. 
Christianization of Syriacs and Armenians most likely began around the 1st century AD. The spread of Christianity beyond Jerusalem is discussed in the Book of Acts.