Let us start in Daniel 2 with Nebuchadnezzar's image because this prophecy seems to lay the framework for the history of man from Daniel's time up to the return of Jesus Christ to this earth. In Daniel 2 we find the Babylonian King Nebuchadnezzar was shown an image made of four different metals. These metals indicated the four, and only four, humanly governed world empires that would arise in the course of man's history from Daniel's day on.
King Nebuchadnezzar was told "Thou art this head of gold" (v.38), relating the head of the image to the Babylonian Empire which flourished around 606-538 BC. After that came the Medo-Persian Empire (538-331 BC), which corresponded to the breast and arms of silver on the image (vs. 32,39). Then followed the Grecian Empire (331-68 BC) led by Alexander the Great, which related to the belly and thighs of bronze (vs.32,39). The last world empire to arise was the Roman Empire (68 BC-476 AD), corresponding to the two legs of iron on the image (vs.33,40). In this way, God revealed through this vision the four world empires which would arise before the kingdom of God would be set up on the earth.
The last parts of the image, its feet and toes, were made of iron and clay, showing that the Roman world would be made up of many different nations from the end of the Roman Empire until Jesus (the stone) came to break in pieces the kingdoms of men, and set up his kingdom on earth (vs.33-35,41-45). So we should expect that the Roman dominion would be made up of many different nations, some strong (iron) and some weak (clay), just before the second advent of the Lord Jesus Christ.