How much of the earth did Nebuchadnezzar's Babylonian empire cover?
Nebuchadnezzar's Babylonian empire covered the then-known earth—the civilized, occupied part of the world at that time. Scripture's phrase 'whole earth' refers to the inhabited earth as it was known then, not the entire globe. The empire ruled by Nebuchadnezzar, his son, and grandson dominated that known region.
Les explains that Babylon, of which Nebuchadnezzar and his son and grandson ruled, was the empire that covered the then known earth—that part of the world that was civilized and occupied. So when Jeremiah 51:7 says Babylon made all the earth drunken, the phrase 'whole earth' means the inhabited earth at that particular time. Les also notes that the nations drank of her wine and became mentally affected, not merely angry. Thus the Babylonian empire's reach is measured by the known, civilized world of that era, not the entire planet.
Babylon hath been a golden cup in the LORD’s hand, that made all the earth drunken: the nations have drunken of her wine; therefore the nations are mad.