Deuteronomy 2:7, 14

The LORD your God has blessed everything you have done; he has protected you while you traveled through this great desert. The LORD your God has been with you for the past forty years, and you have had everything you needed.

It had been thirty-eight years from the time we left Kadesh Barnea until we crossed the Zered Valley. By then, all the fighting men from that time had died, as the LORD had promised would happen.