Joshua made himself flint knives, and circumcised the children of Israel at the hill of the foreskins.
Why did God wait to command the circumcision of the new generation until now rather than on the plains of Moab? Perhaps He did so because He wanted to bring the people into the land before enforcing this aspect of the Law. This is consistent with God’s dealings with humankind. He first gives and then asks (cf. Romans 12:1).