Joshua 5:4-6

5:4 This is why Joshua had to circumcise them: All the men old enough to fight when they left Egypt died on the journey through the desert after they left Egypt. 5:5 Now all the men who left were circumcised, but all the sons born on the journey through the desert after they left Egypt were uncircumcised. 5:6 Indeed, for forty years the Israelites traveled through the desert until all the men old enough to fight when they left Egypt, the ones who had disobeyed the Lord, died off. For the Lord had sworn a solemn oath to them that he would not let them see the land he had sworn on oath to give them, a land rich in milk and honey.