Answer: After the conquest of Canaan, while Joshua was still alive, an altar was built that caused quite a stir and almost led to civil war in the newly founded nation of Israel. When God revealed the Law of Moses, God prohibited the building of altars other than those He had commanded (Deuteronomy 12:1–14). Yet the tribes on the east side of the Jordan River—Reuben, Gad, and the half-tribe of Manasseh—constructed an altar in Joshua 22. As a result, the western tribes felt the Law had been violated and intended to go to war against their own people.

The western tribes had such a strong response to the altar in Joshua 22 because of the command in Deuteronomy 13:12–16: “If you hear it said about one of the towns the Lord your God is giving you to live in that troublemakers have arisen among you and have led the people of their town astray, saying, ‘Let us go and worship other gods’ (gods you have not known), then you must inquire, probe and investigate it thoroughly. And if it is true and it has been proved that this detestable thing has been done among you, you must certainly put to the sword all who live in that town. You must destroy it completely, both its people and its livestock. You are to gather all the plunder of the town into the middle of the public square and completely burn the town and all its plunder as a whole burnt offering to the Lord your God. That town is to remain a ruin forever, never to be rebuilt.”

The tribal leaders west of the Jordan followed this law exactly. In Joshua 22 they heard of an altar; since there was no Mosaic authorization to build such an altar, the western tribes suspected the altar in Joshua 22 represented the beginnings of idolatry. Fortunately for all involved, the western tribes investigated the allegation to discover the truth of the situation before they went to war. As it turned out, the altar built by Reuben, Gad, and the half-tribe of Manasseh was a memorial to the Lord God. The eastern tribes were separated from their brethren by geography, but they wanted to show their spiritual solidarity. They had built the altar on the east side of the Jordan to show their connection to the rest of the Israelites who lived in the Promised Land proper. The altar was a sign of unity, not rebellion.

Joshua 22 concludes the matter of the suspicious altar on a good note: the high priest, Phinehas, says to Reuben, Gad, and Manasseh, “Today we know that the LORD is with us, because you have not been unfaithful to the LORD in this matter. Now you have rescued the Israelites from the LORD’s hand” (Joshua 22:31). Phinehas cleared the eastern tribes of all charges of idolatry. Then, “they were glad to hear the report and praised God. And they talked no more about going to war against them to devastate the country where the Reubenites and the Gadites lived” (Joshua 22:33).

The incident of the altar in Joshua 22 points to the importance of not jumping to conclusions or making assumptions not based on fact. In Nicodemus’ defense of Christ before the Sanhedrin, he emphasizes that the Law does not allow for rash judgments: “Does our law condemn a man without first hearing him to find out what he has been doing?” (John 7:51; cf. Proverbs 18:13).

Later in Israel’s history, after Joshua’s death, idolatry would indeed become a problem for God’s people. The Book of Judges reveals that idol worship soon became common among the Israelites, leading to God’s judgment upon them. Yet, in this early stage of Israel’s possession of the Promised Land, they quickly sought to obey God’s laws and preserve the unity of the tribes (see Psalm 133:1).