It remained powerful and influential for two more centuries, until important setbacks in the 18th and 19th century forced it to cede strategic territories in Europe, which signalled the loss of its former military strength and wealth.After the 1913 Ottoman coup d'état, which effectively put the country under the control of the Three Pashas, the Ottoman Empire decided to join the Central Powers during World War I.In 324, Constantine I chose Byzantium to be the new capital of the Roman Empire, renaming it New Rome.Following the death of Theodosius I in 395 and the permanent division of the Roman Empire between his two sons, the city, which would popularly come to be known as Constantinople, became the capital of the Eastern Roman Empire.Turkey is a secular, unitary, parliamentary republic; slated to transition to a presidential system in 2019, following a 2017 referendum.However, Turkey's current administration headed by president Recep Tayyip Erdoğan of the AKP has enacted measures to increase the influence of Islam, reversed and undermined secularist policies, and has reversed earlier reforms such as Freedom of the Press.
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.
The House of Seljuk was a branch of the Kınık Oğuz 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 latter half of the 11th century, the Seljuk Turks began penetrating into medieval Armenia and the eastern regions of Anatolia.
However, the Byzantines later began using this name to define the Seljuk-controlled parts of Anatolia in the centuries that followed the Battle of Manzikert in 1071.
The medieval Greek and Latin terms did not designate the same geographic area now known as Turkey.