The Islamic Republic of Iran is located between the Caspian Sea and the Persian Gulf, and borders many countries, including Iraq, Turkmenistan, Afghanistan and Pakistan. The country’s unique geography has created a population that is ethnically and linguistically diverse yet religiously almost entirely Muslim. Modern Iran is descended from an ancient civilization dating back to around the tenth century BC, and the area was ruled by Persians, non-Iranian caliphs, Mongol Khans, and Turkic sultans. For centuries, the region has been a center of the Shia branch of Islam. With the Islamic Revolution in 1979, Iran overthrew the ruling monarchy and became an Islamic republic. US-Iranian relations were strained by the hostage situation at the US Embassy in Tehran, and Iran continues to be designated a state sponsor of terrorism and remains subject to US sanctions. The export of oil dominates Iran’s economy and allows it to play an important role in international and regional politics.