Among modern interpreters there is a consensus that the three ribs represent three nations subjugated by the Persians. They also represent the three kingdoms that posed the greatest threat to their power: Lydia, Babylon and Egypt (or some think, Media, Lydia and Babylon). The command to "devour much flesh" emphasizes Persia's superior military might over the peoples from Asia Minor and Egypt to India.
Richard T. Ritenbaugh
Nebuchadnezzar's Image (Part Two): Chest and Arms of Silver
This is a further explanation of the world-ruling empires, showing national characteristics, but this time designed into animals of the same four kingdoms that appear in Daniel 2. Instead of being metals—gold, silver, brass, iron—now we have animals, indicating national characteristics of those four kingdoms, symbolized by the lion, the bear, the leopard, and the beast that was diverse from all the others.
The important thing to note here is that this illustration in Daniel 7 is a parallel of the image seen by Nebuchadnezzar in Daniel 2. This illustration in Daniel 7 confirms that the legs of iron of the Daniel 2 image and the fourth beast of Daniel 7 both exist at Christ's return, fight against Him, and are defeated. So even as the feet and toes of the Daniel 2 image will be at the time of the end, so will this diverse beast. They are one and the same.
John W. Ritenbaugh
Where Is the Beast? (Part 1)
Other Forerunner Commentary entries containing Daniel 7:5: