Afghanistan, officially the Islamic Republic of Afghanistan, is a 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 32 million, composed mostly of ethnic Pashtuns, Tajiks, Hazaras, and Uzbeks.
Humans lived in what is now Afghanistan at least 50,000 years ago. Settled life emerged in the region 9,000 years ago, evolving gradually into the Indus civilization, the Oxus civilization, and the Helmand civilization of the 3rd millennium BCE. Indo-Aryans migrated through Bactria-Margiana area to Gandhara, followed by the rise of the Iron Age Yaz I culture, which has been closely associated with the culture depicted in the Avesta, the ancient religious texts of Zoroastrianism. The region, then known as "Ariana", fell to Achaemenid Persians in the 6th century BCE, who conquered the areas to their east as far as the Indus River.