“Hashem said to Moshe, 'Stretch your hand over the sea. The waters will come back over the Egyptians, covering their chariot and cavalry.' Toward morning, Moshe extended his hand over the sea, and the sea returned to its normal condition. The waters came back and covered the cavalry and chariots. Of all Pharaoh's army that had followed [the Jews] into the sea, not a single one remained.” 14:26-28
One would have expected that the plagues would have sufficiently convinced the Egyptians to recognize that their cause was a lost one and Hashem was on our side. When even that failed, one would have imagined that watching the entire Jewish nation traverse the Sea of Reeds as the waters parted before them, would have caused them to abandon ship. Once again however, the Egyptians stubbornly refused to reach the inevitable conclusion that Hashem controls the world. Their wickedness surpassed only by their foolishness, they plunged headlong into the waters and sank into oblivion.