What does Revelation 16:12 mean?

This verse tells us the sixth angel poured his bowl on the river Euphrates. The contents of the bowl caused the river to dry up. Prior bowl judgments have either corrupted or destroyed most of the water on earth (Revelation 16:1–4). This judgment is not about corrupting or removing the use of this water. Rather, it seems to be about removing a barrier used for defensive purposes: preparing the way for invading kings from the east.

The Euphrates is called "the great river" five times in Scripture. It was the eastern boundary of Israel's inheritance (Deuteronomy 1:7; 11:24). To some extent the river provided protection for Israel because it was difficult to cross and a wilderness to the west separated it from Canaan, the Promised Land. It flows almost 2,000 miles toward Palestine before making its way southeast to the Persian Gulf. In the first century, when Revelation was written, the Euphrates divided East from West, and the kingdoms of China and India lay beyond it to the east.

Centuries earlier, the armies of Cyrus of Persia conquered Babylon by diverting the Euphrates that flowed through the city. They were able to march into Babylon on the dry river bed and capture the city. In the great tribulation, the eastern invader will cross the Euphrates, march through Babylon, and enter Palestine.