Charles Spurgeon Commentary 2 Chronicles 20:27-30

"Then they returned, every man of Judah and Jerusalem, and Jehoshaphat in the forefront of them, to go again to Jerusalem with joy; for Jehovah had made them to rejoice over their enemies. And they came to Jerusalem with psalteries and harps and trumpets unto the house of Jehovah. And the fear of God was on all the kingdoms of the countries, when they heard that Jehovah fought against the enemies of Israel. So the realm of Jehoshaphat was quiet; for his God gave him rest round about." — 2 Chronicles 20:27-30 (ASV)

For the LORD had made them to rejoice over their enemies.

And they came to Jerusalem with psalteries and harps and trumpets unto the house of the LORD. And the fear of God was on all the kingdoms of those countries, when they had heard that the LORD fought against the enemies of Israel. So the realm of Jehoshaphat was quiet: for his God gave him rest round about.

Now, it is a long piece we have read, but I think it would not be complete if I did not read you the song which they sang. In all probability it was Psalm 47. You can almost hear them singing it as they march back.