When Israel do His will, He wars for them, viz. (Exodus 14:14) "The L–rd will war for you." And when they do not do His will, He wars against them, viz. (Isaiah 63:10) "And He turned into a foe of theirs; He warred against them."
When Israel Does God's Will, He Fights on Their Behalf
Mekhilta Tractate Shirah 5:15