From the early Church Fathers to now.
“And four great beasts, different one from another, came up out of the sea.”
“"And four great beasts." As various beasts then were shown to the blessed Daniel, and these different from each other, we should understand that the truth of the narrative deals not with certain beasts, but, under the type and image of different beasts, exhibits the kingdoms that have risen in this world in power over the race of man. For by the great sea he means the whole world.”
“But the prophet, full of disdain for these various metals, sees "four beasts." From those four beasts he understands that those four formidable kingdoms, which will strike fear into all people, will at last have an end, but there will be only one kingdom that will remain for all time without any end, namely, the kingdom that God has prepared for his saints.”
The in-app commentary runs from the Fathers to the early-modern record, then stops — that's where the public-domain sources end, not where the reading does. For the modern reading, follow the sources directly.