So wasn’t Moses married to a Midianite woman? Was she with him, or was she and presumably the rest of her family killed in the war against the Midianites? Or were they Midianites in another region? Also, how was Moses allowed to have a Midianite wife when the rest of the people were judged so severely? Thanks!
Moses’ wife Zipporah was indeed a Midianite. Midian was the son of Abraham by Keturah, the woman he married or took as a concubine after Sarah’s death (see Gen. 25:1–2). At the time of Moses, the Midianites, or at least Zipporah’s father Jethro, were not an enemy but the protector of Israel by protecting Moses. Furthermore, Jethro embraces the worship of Yahweh, at least by the time we read of his sacrifice in Exodus 18:9–12. In other words, this marriage was very similar to Abraham seeking a wife for Isaac from among his own people.
So the Midianites were not always enemies of the Israelites. In fact, being related by blood puts them in the same category as the Moabites (descendants of Lot), which is a group of people that should be sympathetic and helpful to them as their brothers. However, in Numbers 22:4, the Midianites and Moabites band together against the Israelites. Later, the whole group is simply called the “Midianites.” Up until this time, these people would not have been considered enemies at all. The Moabite land, for example, was not to be taken by the Israelites, because Abraham had given it to them (Deut. 2:9).
So the Midianites (at least the ones that had joined with the Moabites) were seeking to harm the Israelites by paying Balaam to curse them. Immediately they have become dangerous enemies because they have fully rejected God and are oppressing the Israelites. Furthermore, Numbers 31:16 makes it clear that Balaam gives them advice for how to bring trouble on Israel by seducing them, not just to marriage but to worship of Baal (Num. 25).
“So Israel joined themselves to Baal of Peor, and the LORD was angry against Israel.” (Num. 25:3). As usual, the sin God is angry with is being led astray into idolatry through marriage. We have several examples of women that are outsiders that join themselves to God and his people instead of seducing their husbands to idols. Zipporah is an example of such a woman. The difference in God’s response is not surprising when we consider the details.