Numbers 31

The Lord told Moses to go seek vengeance on the Midianites for the Israelites. So, Moses had to go to war against his in-laws and their people. Was not Moses wife a Midianite?

When all the Midianite men had been slain the Israelite army returned with their plunder including the Midianite women and children. Among the Midianite men killed were the five Kings of Midian and Balaam son of Beor. The same Balaam who had the talking donkey and blessed the Israelites rather than cursing them as Balak, king of Moab, wished him to.

When the army returned Moses was very angry that the Midianite women had been allowed to live since it was the women who followed Balaam's advice and "intermingled" with the Israelites distracting them from the Lord resulting in a deadly plague. Moses told the soldiers that they could keep all the virgin Midianite women for themselves but all the others must be killed.

After this the spoils (including the livestock and the virgins) were distributed between the Israelites and the army with a percentage going to God via Eleazar and the priests.

So, Balaam (who spoke with God) was advising people to draw the Israelites away from God. Interesting.

Five Kings of Midian Slain by Israel (illustration from the 1728 Figures de la Bible)