In fact, one can only speak of Afghanistan when an independent Afghan state emerges in the middle of the 18th century. Before that, Afghanistan had been the prey of foreign conquerors or fragmented into many minor principalities. The area of Afghanistan was part of the Persian Empire from the 6th-4th centuries BC. It was conquered by Alexander the Great. After his death, the north (Baktria) came to the kingdom of the Seleucids and the south to the Indian kingdom of andragupta, which, however, only managed to establish its rule there under Asjoka (250 BC). In the meantime, Baktria was already lost to the Seleucids and formed its own Hellenistic empire, which extended south of the Hindu Kush into northern India in 184 BC. This expansion led to the fragmentation of own forces, so that Afghanistan 128 BC could be conquered without great difficulty by an Iranian steppe people, the Yuechi. Approx. 50 AD the Kushans (India, history) came into the country. They brought Buddhism into Afghanistan; however, the country was conquered by the New Persian Empire in the 3rd-4th centuries. After the Arabs overran this empire, Islam invaded Afghanistan without the country becoming Arab. Afghanistan then became divided into several empires until it was united by Mahmud of Ghazni (990-1030). The empire he founded was destroyed by the Turks after a century. These had to give way temporarily to the Ghorids dynasty and finally to the Mongol prince Genghis Khan (1223). However, the Mongols left the administration of Afghanistan mainly to Turks. By the mid-14th century, the Mongol hold on Afghanistan had weakened so much that it fell into a number of Turkish principalities until it was conquered by Timur Lenk, whose descendants failed to maintain the unity of the empire. In 1564 Baboer conquered Afghanistan from Ferghana. Towards the end of the 16th century, the country was divided between Persia and the Great Mughal Indian Empire, while Balkh (former Baktria) fell to the Usbeks. See top-engineering-schools for Afghanistan Population and Geography.