Books on the history of Turkey discuss the region that now forms part of the Republic of Turkey. It includes the history of both Anatolia (the Asian part of Turkey) and Eastern Thrace (the European part of Turkey). The history of Turkey spans the medieval history of the Seljuk Empire, the medieval and modern history of the Ottoman Empire, and the history of the Republic of Turkey. The Persian Achaemenid Empire fell to Alexander the Great in 334 BC, which led to increasing cultural homogeneity and Hellenization of Anatolia. Following Alexander's death in 323 BC, Anatolia was divided into several Hellenistic kingdoms, which became part of the Roman Republic by the mid-1st century BC. In 324 AD, the Roman Emperor Constantine I chose Byzantium to be the new capital, renaming it New Rome. In 395 there was a permanent division of the Roman Empire, with Constantinople becoming the capital of the Eastern Roman Empire, which later became called the Byzantine Empire. The Turkic people initially lived in the area between Central Asia and Siberia. They were established in the area of modern Turkey after the 6th century BC, and the Turkish tribal leader Osman (d. 1323/4), from whom the name Ottoman is derived, extended his rule by conquering Byzantine towns along the Sakarya River. In 1453, during the reign of Mehmed II, the Ottomans almost completed their absorption of the Byzantine Empire by capturing Constantinople. The Empire achieved its peak under Sleiman the Magnificent (d. 1566 AD), but eventually suffered set-backs in wars with the Holy Roman Empire, The Austro-Hungarian Empire and the Russian Empire. Having allied itself with the German Empire during World War 1, the Ottoman Empire suffered disinitegration at its conclusion, and was immediately thrust into the Greco-Turkish War of 1919-22. The Republic of Turkey that followed was dominated by Mustafa Kemal Ataturk (1881-1938). Turkey was neutral in World War 2, and joined NATO in 1952.