With Kingdoms starting to form around 3200-2800 BC, Iran was first unified under the Median Empire of 678-549 BC. Under Cyrus the Great, Iran reached its largest Geographic incarnation as the Achaemenid Empire (550-330 BC) as we started experimenting with centralised bureaucracy, postal systems, road systems and official languages. It's peak population was about 44% of those on the planet. After several Empires came and went, the Arab Rashudin Caliphate brought Islam. The blossoming of literature, medicine, art and philosophy saw Iran at the centre of the Islamic Golden Age. In the 12th century, it is estimated that about three quarters of the population died in the Mongol Invasions of Genghis Khan. In the 1500s, Ismail I led a conversion to Shia Islam and Modern Iran is the only official Shia nation in the world. An Anglo-American sponsored coup in 1953 put Iran at the centre of the cold war. In 1979, the Islamic Revolution led to Iran becoming an officially Islamic Republic.