I have heard that in combat, it is best to let opposing forces destroy each other prior to stepping into the fray
2 Chronicles 20:20-23
20 They rose early in the morning and went out to the wilderness of Tekoa; and when they went out, Jehoshaphat stood and said, “Listen to me, O Judah and inhabitants of Jerusalem, put your trust in the Lord your God and you will be established. Put your trust in His prophets and succeed.”
21 When he had consulted with the people, he appointed those who sang to the Lord and those who praised Him in holy attire, as they went out before the army and said, “Give thanks to the Lord, for His lovingkindness is everlasting.”
22 When they began singing and praising, the Lord set ambushes against the sons of Ammon, Moab and Mount Seir, who had come against Judah; so they were routed.
23 For the sons of Ammon and Moab rose up against the inhabitants of Mount Seir destroying them completely; and when they had finished with the inhabitants of Seir, they helped to destroy one another.