As for the ram that you saw with the two horns, these are the kings of Media and Persia.
We have previously given a brief explanation of all these subjects. But here the angel removes all doubt, lest we should still anxiously inquire the meaning of the ram which Daniel saw, and of the he-goat which followed and prostrated the ram. The angel, therefore, here pronounces the ram to represent two kingdoms, which coalesced in one.
Daniel sought understanding and did not seek in vain. Those who truly know God's things must desire to know more of them. When Gabriel approached, Daniel fell in fear and then into deep sleep, not from carelessness but from the weight of such abundance of revelations.
AI summary
Commenting on Daniel 8:15-27
The ram which thou sawest having two horns,.... Here begins the particular explanation of the above vision, and of the first thing which the prophet saw in it, a ram with two horns: which two horns, he says, are the kings of Media and Persia; Darius the first king was a Mede, and Cyrus, that succeeded him, or rather reigned with him, was a Persian...