The Reubenites, the Gadites, and the half-tribe of Manasseh had valiant men who carried shield and sword, and drew the bow, expert in war, 44,760, able to go to war. They waged war against the Hagrites, Jetur, Naphish, and Nodab. And when they prevailed over them, the Hagrites and all who were with them were given into their hands, for they cried out to God in the battle, and he granted their urgent plea because they trusted in him. They carried off their livestock: 50,000 of their camels, 250,000 sheep, 2,000 donkeys, and 100,000 men alive. For many fell, because the war was of God. And they lived in their place until the exile. 1 Chronicles 5:18-22.
We don’t know much about this conflict, but it appears that it was not of the Jews’ choosing. After all it says that they made war with these people but that they called out urgently to their God. This urgency may be because they were on the losing end for a while. But then the Lord turned it around for them. God may have set up this conflict because he wanted to punish this group of idolaters and drive them from the land. After all, that is what he had commanded them to do.