Before the establishment of the Republic of Turkey, Ankara was a small city, and by 2009, it had developed into a modern city of about 5 million people, second only to the economic center and the ancient capital of Istanbul. The city of Ankara is divided into two parts, the old city is centered on an ancient castle built on a small hill; the new city is surrounded by the east, west and south of the old city. Before Ankara was officially designated the capital, the city was not large and only tens of thousands of residents. During the prestigious Ottoman period, Turkey's capital was Istanbul on the edge of the Bosphorus. With the decline of the Ottoman Empire and the invasion of imperialist forces such as Russia, Britain, and France, Turkey was at risk of partition by the end of the 19th and early 20th centuries. Istanbul, the capital, was also often under threat from the gunships of European imperialist powers. Mustafa Kemal, revered as the "father of Turkey", went to Asia Minor to organize a bourgeois revolution against foreign aggression and overthrow the feudal imperialism of Sudan internally. Due to its moderate geographical location and convenient transportation, Ankara gradually became the center of the struggle. And, for security reasons, Ankara was designated the capital of the Republic after the victory of the revolution.