Daniel 8:20 (ESV)

20 As for the ram that you saw with the two horns, these are the kings of Media and Persia.

With regards to the ram with the two horns, we are reminded of the kingdom of the Medes and Persians. The horn that is the longest or the greatest represents the Persians. The Persians become more powerful in the empire than the Medes. The Medo-Persian Empire will expand from the tribal area of the Persians to the west, north and south. Thus, they will take over power from the Babylonians. When the armies of the Medes and Persians stand at the gate of the palace in Babylon, it comes as no surprise to Daniel. He sees how the Lord is active in carrying out his plan. Babylon cannot stop it, for the Medes and Persians have become supreme.