Turkey (officially the Republic of Turkey), is a parliamentary republic largely located in Western Asia with the portion of Eastern Thrace in Southeastern Europe. Turkey is bordered by eight countries: Bulgaria to the northwest; Greece to the west; Georgia to the northeast; Armenia, Iran and the Azerbaijani exclave of Nakhchivan to the east; and Iraq and Syria to the south. The Mediterranean Sea is to the south; the Aegean Sea to the west; and the Black Sea to the north. The Sea of Marmara, the Bosphorus and the Dardanelles (which together form the Turkish Straits) demarcate the boundary between Thrace and Anatolia; they also separate Europe and Asia. Turkey's location at the crossroads of Europe and Asia makes it a country of significant geostrategic importance.
Turkey has been inhabited since the paleolithic age, including various ancient Anatolian civilizations, Aeolian and Ionian Greeks, Thracians, and Persians. After Alexander the Great's conquest, the area was Hellenized, which continued with the Roman rule and the transition into the Byzantine Empire. The Seljuk Turks began migrating into the area in the 11th century, starting the process of Turkification, which was greatly accelerated by the Seljuk victory over the Byzantines at the Battle of Manzikert in 1071. The Seljuk Sultanate of Rûm ruled Anatolia until the Mongol invasion in 1243, upon which it disintegrated into several small Turkish beyliks.
Starting from the late 13th century, the Ottomans united Anatolia and created an empire encompassing much of Southeastern Europe, Western Asia and North Africa, becoming a major power in Eurasia and Africa during the early modern period. The empire reached the peak of its power between the 15th and 17th centuries, especially during the 1520-66 reign of Suleiman the Magnificent. After the second Ottoman siege of Vienna in 1683 and the end of the Great Turkish War in 1699, the Ottoman Empire entered a long period of decline. The Tanzimat reforms of the 19th century, which aimed to modernize the Ottoman state, proved to be inadequate in most fields, and failed to stop the dissolution of the empire. The Ottoman Empire entered World War I (1914-18) on the side of the Central Powers and was ultimately defeated. During the war, major atrocities were committed by the Ottoman government against the Armenians, Assyrians and Pontic Greeks. Following WWI, the huge conglomeration of territories and peoples that formerly comprised the Ottoman Empire was divided into several new states. The Turkish War of Independence (1919-22), initiated by Mustafa Kemal Atatürk and his colleagues in Anatolia, resulted in the establishment of the modern Republic of Turkey in 1923, with Atatürk as its first president.