Joshua 5:4, 6

And this is the reason why Joshua circumcised them: all the males of the people who came out of Egypt, all the men of war, had died in the wilderness on the way after they had come out of Egypt.

For the people of Israel walked forty years in the wilderness, until all the nation, the men of war who came out of Egypt, perished, because they did not obey the voice of the LORD; the LORD swore to them that he would not let them see the land that the LORD had sworn to their fathers to give to us, a land flowing with milk and honey.