John Gill Commentary 2 Chronicles 21:16

"And Jehovah stirred up against Jehoram the spirit of the Philistines, and of the Arabians that are beside the Ethiopians:" — 2 Chronicles 21:16 (ASV)

Moreover, the Lord stirred up against Jehoram the spirit of
the Philistines
Which had been depressed in the times of Jehoshaphat, to whom they brought their presents and tribute willingly, (2 Chronicles 17:11)

and of the Arabians that were near the Ethiopians ;
not the Ethiopians of Africa, as the Targum, for the Arabians were not near them, but the Chusaean Arabs or Midianites, see (Numbers 12:1) . The Targum is, the Word of the Lord did this.