Several ecumenical councils of the early Church were held in cities located in present-day Turkey including the First Council of Nicaea (Iznik) in 325, the First Council of Constantinople (Istanbul) in 381, the Council of Ephesus in 431, and the Council of Chalcedon (Kadıköy) in 451.
Seljuks and the Ottoman Empire:
The House of Seljuk originated from the Kınık branch of the Oghuz Turks who resided on the periphery of the Muslim world, in the Yabgu Khaganate of the Oğuz confederacy, to the north of the Caspian and Aral Seas, in the 9th century. In the 10th century, the Seljuks started migrating from their ancestral homeland into Persia, which became the administrative core of the Great Seljuk Empire, after its foundation by Tughril.
In the latter half of the 11th century, the Seljuk Turks began penetrating into medieval Armenia and the eastern regions of Anatolia. In 1071, the Seljuks defeated the Byzantines at the Battle of Manzikert, starting the Turkification process in the area; the Turkish language and Islam were introduced to Armenia and Anatolia, gradually spreading throughout the region. The slow transition from a predominantly Christian and Greek-speaking Anatolia to a predominantly Muslim and Turkish-speaking one was underway. The Mevlevi Order of dervishes, which was established in Konya during the 13th century by Sufi poet Celaleddin Rumi, played a significant role in the Islamization of the diverse people of Anatolia who had previously been Hellenized. Thus, alongside the Turkification of the territory, the culturally Persianized Seljuks set the basis for a Turko-Persian principal culture in Anatolia, which their eventual successors, the Ottomans, would take over.
In 1243, the Seljuk armies were defeated by the Mongols at the Battle of Köse Dağ, causing the Seljuk Empire’s power to slowly disintegrate. In its wake, one of the Turkish principalities governed by Osman I would evolve over the next 200 years into the Ottoman Empire. The Ottomans completed their conquest of the Byzantine Empire by capturing its capital, Constantinople, in 1453: their commander thenceforth being known as Mehmed the Conqueror.
In 1514, Sultan Selim I (1512–1520) successfully expanded the empire’s southern and eastern borders by defeating Shah Ismail I of the Safavid dynasty in the Battle of Chaldiran. In 1517, Selim I expanded Ottoman rule into Algeria and Egypt, and created a naval presence in the Red Sea. Subsequently, a contest started between the Ottoman and Portuguese empires to become the dominant sea power in the Indian Ocean, with a number of naval battles in the Red Sea, the Arabian Sea and the Persian Gulf. The Portuguese presence in the Indian Ocean was perceived as a threat to the Ottoman monopoly over the ancient trade routes between East Asia and Western Europe. Despite the increasingly prominent European presence, the Ottoman Empire’s trade with the east continued to flourish until the second half of the 18th century.
The Ottoman Empire’s power and prestige peaked in the 16th and 17th centuries, particularly during the reign of Suleiman the Magnificent, who personally instituted major legislative changes relating to society, education, taxation and criminal law.
The Ottoman Navy contended with several Holy Leagues, such as those in 1538, 1571, 1684 and 1717 (composed primarily of Habsburg Spain, the Republic of Genoa, the Republic of Venice, the Knights of St. John, the Papal States, the Grand Duchy of Tuscany and the Duchy of Savoy), for the control of the Mediterranean Sea.