Joshua 5:4, 6-7

Joshua had to circumcise them because all the men who were old enough to fight in battle when they left Egypt had died in the wilderness.

The Israelites had traveled in the wilderness for forty years until all the men who were old enough to fight in battle when they left Egypt had died. For they had disobeyed the LORD, and the LORD vowed he would not let them enter the land he had sworn to give us—a land flowing with milk and honey. So Joshua circumcised their sons—those who had grown up to take their fathers’ places—for they had not been circumcised on the way to the Promised Land.