The officers said to Moses "Not one man is missing from us."
The war against Midian was a war against baseless hatred and strife. G-d commands us to wage this war constantly, in order that hatred, discord, and spite be replaced by loving-kindness, concord, and altruism. Besides the obvious benefits for us as individuals and as a society, G-d "benefits" from this struggle as well. As the Talmudic sage Rabbi Akiva said, brotherly love is the foundation of the entire Torah.
G-d assures us that in our ongoing war against hatred -- just as was the case with the original war against Midian -- we will ultimately not suffer any losses: physical, spiritual, or even financial.
--From Kehot's Daily Wisdom