From the late 10th to the late seventh century BC, the Iranian peoples, together with the “pre-Iranian” kingdoms, fell under the domination of the Assyrian Empire, based in northern Mesopotamia. Under king Cyaxares, the Medes and Persians entered into an alliance with Babylonian ruler Nabopolassar, as well as the fellow Iranian Scythians and Cimmerians, and together they attacked the Assyrian Empire. The civil war ravaged the Assyrian Empire between 616 and 605 BC, thus freeing their respective peoples from three centuries of Assyrian rule. The unification of the Median tribes under king Deioces in 728 BC led to the foundation of the Median Empire which, by 612 BC, controlled almost the entire territory of present-day Iran and eastern Anatolia. This marked the end of the Kingdom of Urartu as well, which was subsequently conquered and dissolved.
In 550 BC, Cyrus the Great, the son of Mandane and Cambyses I, took over the Median Empire, and founded the Achaemenid Empire by unifying other city-states. The conquest of Media was a result of what is called the Persian Revolt. The brouhaha was initially triggered by the actions of the Median ruler Astyages, and was quickly spread to other provinces, as they allied with the Persians. Later conquests under Cyrus and his successors expanded the empire to include Lydia, Babylon, Egypt, parts of the Balkans and Eastern Europe proper, as well as the lands to the west of the Indus and Oxus rivers.
539 BC was the year in which Persian forces defeated the Babylonian army at Opis, and marked the end of around four centuries of Mesopotamian domination of the region by conquering the Neo-Babylonian Empire. Cyrus entered Babylon and presented himself as a traditional Mesopotamian monarch. Subsequent Achaemenid art and iconography reflect the influence of the new political reality in Mesopotamia.
At its greatest extent, the Achaemenid Empire included territories of modern-day Iran, Republic of Azerbaijan (Arran and Shirvan), Armenia, Georgia, Turkey (Anatolia), much of the Black Sea coastal regions, northeastern Greece and southern Bulgaria (Thrace), northern Greece and North Macedonia (Paeonia and Macedon), Iraq, Syria, Lebanon, Jordan, Israel and the Palestinian territories, all significant population centers of ancient Egypt as far west as Libya, Kuwait, northern Saudi Arabia, parts of the United Arab Emirates and Oman, Pakistan, Afghanistan, and much of Central Asia, making it the first world government and the largest empire the world had yet seen.
It is estimated that in 480 BC, 50 million people lived in the Achaemenid Empire. The empire at its peak ruled over 44% of the world’s population, the highest such figure for any empire in history.
The Achaemenid Empire is noted for the release of the Jewish exiles in Babylon, building infrastructures such as the Royal Road and the Chapar (postal service), and the use of an official language, Imperial Aramaic, throughout its territories. The empire had a centralized, bureaucratic administration under the emperor, a large professional army, and civil services, inspiring similar developments in later empires.