The sea — The dead sea, beyond which mount Seir lay. Syria — Largely so called, and so it includes the Moabites and Ammonites. And it may be thus expressed, to intimate that they came by the instigation of the Syrians, to revenge themselves of Jehoshaphat for joining with Ahab against them.
Related Commentaries of 2 Chronicles 20:2
2 Chronicles 20:2
2 Then there came some that told Jehoshaphat, saying, There cometh a great multitude against thee from beyond the sea on this side Syria; and, behold, they be in Hazazontamar, which is Engedi.