Christianity began with Jesus Christ in Judea, with his historical existence and crucifixion widely accepted. Early spread is attributed to apostles and Paul, who converted many across the Roman Empire. By 100 AD, the four gospels were complete, forming the foundation of Christianity.

Armenia became the first Christian country around 301 AD. Despite early persecution, Roman Emperor Constantine legalized Christianity in 312 AD, and it later became the state religion. The Council of Nicaea in 325 AD established the Nicene Creed. Christianity also spread into Africa, with Axom adopting it as its official religion around 330 AD.

Barbarian tribes largely converted to Christianity. St. Jerome completed the Vulgate Bible around 405 AD, which became the official Catholic text. Missionaries like St. Patrick and Columba converted Ireland and Scotland. The Great Schism in 1054 split Christianity into the Eastern Orthodox and Roman Catholic Churches. Crusades were launched to reclaim the Holy Land, and eventually, the Ottoman Turks captured Constantinople in 1453.

The age of discovery in the 15th century saw European powers spread Christianity globally. Portugal brought it to the Kingdom of Congo in 1482, and Christopher Columbus's arrival in the Americas in 1492 marked a significant moment for its spread. Spain and Portugal forcibly converted indigenous peoples in the Americas, and Christianity expanded in West Africa via the slave trade.

In 1517, Martin Luther initiated the Protestant Reformation, challenging the Catholic Church and leading to the rise of various Protestant denominations across Northern Europe. Meanwhile, Catholic missionaries like Francis Xavier spread Christianity to Southeast Asia and Japan. English and Dutch Protestants established colonies in North America, often seeking religious freedom.

The 18th century saw religious revivals known as the Great Awakenings in Britain and the US, fostering the evangelical movement. European imperialism in the 19th century further spread Christianity to Australia, Polynesia, New Zealand, and India through settlers and missionaries like William Carey and David Livingstone. This era also saw resistance and backlash, such as the Indian Uprising of 1857.

By the late 19th century, Christianity rapidly grew in Korea, and European colonization brought it to 90% of Africa by 1914. Despite initial resistance and violent backlashes like the Boxer Rebellion, missionary work led to millions of converts in China. The rise of communism in the 20th century posed a threat, but Christianity proved resilient, re-emerging with popular support after the fall of communist governments. Today, Christianity remains the most practiced religion globally.