The Islamic Republic of Iran, sometimes known as Persia, is a nation in Southwest Asia. Its capital and largest city is Tehran. Iran is home to 75 million people, most of whom are Persians and Shiites. Iran derives much of its income from its petroleum reserves in the Persian Gulf. Since 1979, it has been ruled as a authoritarian theocracy and has come into frequent conflict with the West, primarily the United States.
In the 6th century BC, Cyrus the Great created the first empire in world history, the Achaemenid Empire. He conquered most of Mesopotamia, as well as Iran proper. He was known for his tolerant rule. His son, Cambyses, conquered Egypt. In the 5th century, Darius I invaded Greece in retaliation for Greek support for an Ionian revolt, beginning the Greco-Persian Wars. The first invasion was repelled at the Battle of Marathon. Darius' son, Xerxes I, invaded Greece again, and was defeated at the battles of Thermopylae, Salamis, and Plataea.
In the 3rd century, Persia was invaded by Alexander the Great and swiftly defeated. The Achaemenids were replaced with the Seleucid dynasty, named for Seleucus I. The Seleucids were later replaced by the Parthian Empire. The Parthians fought several wars with Rome, before they were defeated, and the Sassanid dynasty took over. The Sassanids clashed with both Rome and its successor, the Byzantines. In the 7th century, the Sassanids were decisively defeated by the Arabs, and converted to Islam.
In the 13th century, the Khwarezmid Empire ruled Persia. They angered the Mongols by killing diplomats, and were invaded and devastated. When the Mongol Empire fractured, the Ilkhanate took over the Persia. The Ilkhanate was invaded by Timur in the 14th century, and Timur and his descendants ruled Persia until the 16th century.
The Safavid dynasty was the first dynasty to restore meaningful independence to Persia. They clashed frequently with the Russian Empire along their shared Central Asian border. The Pahlavi dynasty was the last dynasty to rule Iran, which had been renamed from Persia in 1930. During World War II, the United Kingdom invaded them to secure their oil deposits. In the 1950s, a progressive prime minister came to power, and nationalized the British oil companies there. A joint United States-United Kingdom overthrew him and reinstated the Shah.
In 1980, Iraq under Saddam Hussein invaded, starting the Iran-Iraq War. Iraq received military assistance from the United States, but they were unable to capitalize on their victories. The bloody war ended in 1988 with nothing gained by either side. In the 2000s, Iran began a nuclear program, ostensibly for civilian use only. The United Nations has enacted numerous sanctions against Iran, but the program has continued.
Iran is bordered to the northwest by Azerbaijan, to the west by Iraq, to the north by the Caspian Sea and Turkmenistan, to the east by Pakistan and Afghanistan, and to the south by the Persian Gulf. Most of Iran is a hot, dry plateau. The Zagros and Alborz mountains rise in the northwest, where Tehran is located. The Kara Kum desert of Turkmenistan also spreads into northeastern Iran.