No battle, no cursing. All the Moabites had left was to entice the Israelites to compromise. It’s blamed on Balam:
Revelation 2:14 …. Balaam, who showed Balak how to trip up the people of Israel. He taught them to sin by eating food offered to idols and by committing sexual sin …
The Israelites fell for it.
Let’s face it, after almost 40 years of wandering in the desert and living on manna, with occasional feasts of quail and their own livestock, most of us would see an offer of a feast as a foretaste of the promised land of milk and honey.
Who would have suspected the feasting in itself was worship of the Moabite gods (Baal)? The ringleaders, no doubt, had been invited to the feasts by those beautiful and oh-so-accommodating Moabite women they had been seeing (the Midianites were living with the Moabites at this stage, and worked with the Moabites on this). The rest just followed.
We don’t know how long it went on for, but it was long enough for someone to think it would be fine to bring a Midianite woman back to the camp, in front of everyone. It wasn’t the best of timing, since it was right in the middle of a reprimand from God: people were dying from a plague and the ringleaders were being executed.
The Israelites had spent close to 40 years learning from God that they were holy because He is Holy, and that they should live separated from the other peoples, forbidden to marry them. Then so close to the end of their journey, they do this. It was close to a final straw for God.
The only real positive to come out of all this was, even after a plague that killed some 24,000 people, there were about as many Israelite males of fighting age as there had been some 40 years earlier. We would also like to hope that there were no more compromisers, complainers or idolators left to dissuade the Israelites from entering their promised land.