The history of modern Christianity spans from the early 15th century to the end of World War II, initiating its early modern period around 1500 with the Protestant Reformation and the Age of Exploration. This era witnessed Christianity's significant global expansion, ultimately establishing it as the world's largest religion.

A pivotal moment for Eastern Orthodoxy occurred in 1453 with the fall of Constantinople to the Ottoman Empire. Under Ottoman Islamic rule, the Greek Orthodox Church surprisingly acquired substantial administrative and civil power as an autonomous "millet," with the Ecumenical Patriarch serving as the religious and administrative leader for all Orthodox subjects.

However, this unique arrangement led to the Orthodox communion's four-hundred-year isolation from the West. Consequently, Eastern Orthodoxy remained largely detached from the theological debates of the Western Reformation and Counter-Reformation. Despite these formal privileges, Christians in Ottoman territories often experienced the realities of second-class citizenship and local corruption.