We transition from the rules commanding the sacrifices to a situation where God is asking Moses to go into battle and telling him exactly how many troops and what his strategy ought to be when he goes into battle. So they went to battle against the Midianites and they won, as we would expect. They also brought back some booty to Moses in order to show what exactly they had done and how they had conquered. With Moses in the battle is Eleazar who is now the high priest and the grandson of Aaron. We saw him before.
Well, Moses was not pleased that they had kept the women alive because they were part of that time when the men of Israel had turned their back on God to pursue the women of Midian and Eleazar had driven a spear through that Israelite man and that Midianite woman. So, all the women were killed except those who had not slept with an Israelite in the past. I know, hard to follow and hard to stomach.
But remember this was in order to ensure that the people of Israel were pure and that they had everything that they needed in order to be obedient to God, and to pass that obedience on to their children. All was divided and so the chapter ends.