Contradiction with Genesis 11:1-9
This passage describes the Tower of Babel, where God confused the languages of people and scattered them, contradicting the idea of kings from the East unifying or crossing the Euphrates freely as implied in Revelation 16:12.
Genesis 11:1-9: And the whole earth was of one language, and of one speech. [language: Heb. lip.] [speech: Heb. words]
Contradiction with Isaiah 11:15-16
This passage describes God drying up the Euphrates to make a way for the return of His people, but with a positive connotation, whereas Revelation 16:12 describes a preparation for battle.
Isaiah 11:15-16: And the LORD shall utterly destroy the tongue of the Egyptian sea; and with his mighty wind shall he shake his hand over the river, and shall smite it in the seven streams, and make [men] go over dryshod. [dryshod: Heb. in shoes]
Contradiction with Jeremiah 51:36
Here, God promises to dry up Babylon's sea as part of its destruction, while Revelation 16:12's drying up of the Euphrates is to prepare for invasion, implying a different context and purpose.
Jeremiah 51:36: Therefore thus saith the LORD; Behold, I will plead thy cause, and take vengeance for thee; and I will dry up her sea, and make her springs dry.