Adam Clarke on Daniel 7:3

Four great beasts came up from the sea - The term sea, in Hebrew ים yam, from המה hamah, to be tumultuous, agitated, etc., seems to be used here to point out the then known terraqueous globe, because of its generally agitated state; and the four winds striving, point out those predatory wars that prevailed almost universally among men, from the days of Nimrod, the founder of the Assyrian or Babylonish monarchy, down to that time, and in the end gave birth to the four great monarchies which are the subject of this vision.

Diverse one from another - The people were different; the laws and customs different; and the administration of each differently executed.