After this, the Moabites and Ammonites with some of the Meunites came to make war on Jehoshaphat. Why? Did Jehoshaphat do something wrong to them or hurt them? Alarmed, Jehoshaphat resolved to inquire of the LORD, and he proclaimed a fast for all Judah. The people of Judah came together to seek help from the LORD; indeed, they came from every town in Judah to seek him. All the men of Judah, with their wives and children and little ones, stood there before the LORD. Then the Spirit of the LORD came upon Jahaziel son of Zechariah, the son of Benaiah, the son of Jeiel, the son of Mattaniah, a Levite and descendant of Asaph, as he stood in the assembly.
He said: "Listen, King Jehoshaphat and all who live in Judah and Jerusalem! This is what the LORD says to you: 'Do not be afraid or discouraged because of this vast army. For the battle is not yours, but God's. Tomorrow march down against them. They will be climbing up by the Pass of Ziz, and you will find them at the end of the gorge in the Desert of Jeruel. You will not have to fight this battle. Take up your positions; stand firm and see the deliverance the LORD will give you, O Judah and Jerusalem. Do not be afraid; do not be discouraged. Go out to face them tomorrow, and the LORD will be with you.' "
Jehoshaphat bowed with his face to the ground, and all the people of Judah and Jerusalem fell down in worship before the LORD. Then some Levites from the Kohathites and Korahites stood up and praised the LORD, the God of Israel, with very loud voice.
Early in the morning they left for the Desert of Tekoa. As they set out, Jehoshaphat stood and said, "Listen to me, Judah and people of Jerusalem! Have faith in the LORD your God and you will be upheld; have faith in his prophets and you will be successful."
As they began to sing and praise, the LORD set ambushes against the men of Ammon and Moab and Mount Seir who were invading Judah, and they were defeated. The men of Ammon and Moab rose up against the men from Mount Seir to destroy and annihilate them. After they finished slaughtering the men from Seir, they helped to destroy one another. God works in amazing ways. I'd say that would be fun to watch.