The Lord God will stretch out his hand against Assyria, and cause his servant Nebuchadnezzar to stretch out his hand to conquer this most powerful nation in the region. This prophecy about Assyria’s destruction uses the most graphic language to describe the ruined state she will be brought to.
It doesn't matter how great the land; no land will escape this coming judgment of God. We can see that this is more than what the Chaldeans will do. All the time Zephaniah speaks of two judgments: the judgment of Judah, and then an even greater judgment one day from which no one will escape: the judgment of Judah is a picture in turn of the great final judgment that will come.