Afghanistan, officially the Islamic Republic of Afghanistan, is a mountainous landlocked country at the crossroads of Central and South Asia. Afghanistan is bordered by Pakistan to the east and south, Iran to the west, Turkmenistan, Uzbekistan, and Tajikistan to the north, and China to the northeast. Occupying 652,000 square kilometers, it is a mountainous country with plains in the north and southwest. Kabul is the capital and largest city. Its population is around 39 million, composed mostly of ethnic Pashtuns, Tajiks, Hazaras, and Uzbeks. Humans lived in what is now Afghanistan at least 50,000 years ago.