BABYLON - As the head of Gold, King Nebuchadnezzar understood that this was a representation of his rulership. It should also be understood that kings are synonymous with their kingdoms, therefore the head is also symbolic of the Babylonian Empire. Babylon's supremacy lasted approximately from 626 BC to 539 BC.
MEDO-PERSIA - As the nation that conquered Babylon and the known world, the arms and chest of silver represented the Medo-Persian Empire. Eventually, Persia would conquer Media to become the sole world power. Its supremacy lasted from 539 BC to 331 BC.
GREECE - As the belly and thighs of bronze, Greece consisted of Alexander the Great's empire, but also the four divisions that it broke into after the Greek king's death—Macedonia, Asia Minor, Ptolemaic Egypt, and Syria and the eastern nations. The Hellenistic supremacy lasted from 331 BC to 168 BC.
PAGAN ROME - Imperial Rome is the fourth and final world power on this prophetic spectrum. According to Daniel 2:40, the nation represented as iron legs would break and bruise the known world. There are multiple phases to this world power, however the Pagan phase would rule the known world from 168 BC to 538 AD.
PAPAL ROME - As the second phase of Rome, this religious system represented by the Clay in the feet and toes shows that it's principles would be mixed with the nations of this world. The Papacy came to power in 538 AD and lost its hold over church and state in 1798 AD.