Peter Pett's Commentary on the Bible
Joshua 22 - Introduction
Chapter 22 The Transjordan Contingents Return Home - The Memorial Altar.
The initial war with the Canaanites being over, Joshua called to him the warriors from the two tribes of Reuben and Gad, and the half tribe of Manasseh, who had came over Jordan with him to assist in the warfare, and commended them for their obedience to Moses, to himself, and to God. Then he bade them return home with his blessing on them, giving them careful instructions about keeping to the right ways and to the rightful worship of God.
At this they returned to their country, and when they came to the border they set up a memorial altar by the River Jordan. When the rest of the children of Israel heard of this, it gave them great offence, for they feared that they were going to turn from the pure worship of God at the central sanctuary. So they sent a deputation of princes to them, along with Phinehas, the son of Eliezer, the high priest, to enquire into what was happening, and rebuke them about it. But when they received a satisfactory answer, they returned and reported back to the children of Israel to the satisfaction of all.