What does Joshua 22:19 mean?

If your land is somehow unclean, come over to the Lord’s land, where his tent is, and settle with us. But don’t rebel against the Lord or build another altar besides the one we have for him. Joshua 22:19 - Modern Text Bible

(They offer a solution: if there’s a problem with their land, they can move, but they must not create a rival altar or break unity with God.)