Turkey is a Eurasian country that stretches across the Anatolian peninsula in southwestern Asia and the Balkan region of southeastern Europe. The region comprising modern Turkey has seen the birth of major civilisations including the Byzantine and Ottoman Empires. Owing to its strategic location at the intersection of two continents, Turkey's culture is a unique blend of Eastern and Western tradition, often described as a bridge between the two civilisations. Turkey is a democratic, secular, unitary, constitutional republic whose political system was established in 1923 under the leadership of Mustafa Kemal Atatürk following the fall of the Ottoman Empire in the aftermath of World War I. Since then, Turkey has increasingly integrated with the West while continuing to foster relations with the Eastern world. It is a founding member of the United Nations, the Organisation of the Islamic Conference (now the Organisation of Islamic Cooperation), the Organisation for Economic Co-operation and Development and the Organization for Security and Co-operation in Europe, a member state of the Council of Europe since 1949 and of NATO since 1952. Since 2005, Turkey has been in accession negotiations with the European Union, having been an associate member since 1963. Turkey is also a member of the G20 which brings together the 20 largest economies of the world.