Revelation 15 showed us seven angels receiving bowls of wrath, and Revelation 16 shows the angels pouring out their bowls, including this one,
“Then the sixth angel poured out his bowl on the great river Euphrates, and its water was dried up, so that the way of the kings from the east might be prepared” (Revelation 16:12).
The Euphrates was a great barrier, which hindered the kings of the east from gathering for the battle of the great day of God. Revelation 9:14 showed that the sixth trumpet of judgment revealed four angels bound at the great river Euphrates, and with the blowing of the trumpet they were released to kill a third of mankind. With this bowl, the water was dried up.
The Euphrates was no longer serving as a barrier, but would allow free movement from the east.
Later, John will introduce us to Babylon, which was east of Jerusalem. Babylon is a symbol for Rome and Jerusalem is a symbol for the church.
Therefore, the Euphrates represented a barrier that prevented Rome from attacking the church further or fully.
However, with this bowl that barrier was removed, so that a new Babylon, which would be another form of Rome, was enabled to attack the church. That may not sound like a judgment against the beast, but it was because it allowed the beast and his partners to gather for their own slaughter at Armageddon, which John will show shortly, and that occupies the next couple of chapters.