During the second millennia B.C., successive Indo-European (Aryan) invaders broke through into the Iranian plateau, either from the Caucasus, or through Central Asia. Those who settled in Iran were divided into tribes that were distinguished from each other by their different dialects. The most famous of these tribes were the Persians (Parsa), and the Medes (Mada). 

The Persians eventually settled in the province of Fars and in the Bakhtiari Mountains, while the Medes occupied the Hamedan plain. The Medes, were fierce warriors and skilled horse breeders, and at first were organised as independent tribes; however, this changed under the tribal chief, Deioces. The Median capital was established at Ecbatana or "Place of Assembly", modern Hamedan. Under the rule of Cyaxares (633-584 B.C.), the Medes put an end to centuries of war against the Assyrians. Their capture of Niniva in 612 B.C. finally brought down the Assyrian Empire. For more than half a century after the fall of Niniva, the Medes ruled over a vast empire with borders stretching from Afghanistan to Turkey.