While King Nebuchadnezzar was a supreme unrestricted ruler, the Medo-Persian Empire which followed was inferior in the fact that it was a limited monarchy where the ruling kings were bound by the laws they enacted.

The third kingdom, the Greek Empire, did begin an absolute monarchy with Alexander the Great, but upon his death his kingdom was divided. The Diadochi (from Greek: Διάδοχοι, Diadokhoi, meaning “Successors”) were the rival generals, families and friends of Alexander the Great who fought for control over his empire.

In time the Greek Empire developed into a democracy and there was no longer a monarchy. Therefore in terms of rulership, the third kingdom of Greece was inferior to that of the Medes and the Persians, whose empire was inferior to that of King Nebuchadnezzar.

The fourth kingdom is symbolized by iron. History tells us that this is the Roman Empire which conquered Greece. The first three kingdoms existed in Daniel's day, but Rome did not. So Daniel did not identify it directly by name. Rome was known as the “Iron Monarchy.” The Latin word “Rome” means strength and iron is the strongest of the metals.