Adam Clarke on Joshua 22:12

To go up to war against them - Supposing that they had built this altar in opposition to that which Moses, by the command of God, had erected, and were consequently become rebels against God and the Israelitish constitution, and should be treated as such. Their great concern for the glory of God led them to take this step, which at first view might appear precipitate; but, that they might do nothing rashly, they first sent Phinehas and ten princes, one out of each tribe, to require an explanation of their motives in erecting this altar.