The population of Afghanistan is around 37,466,414 as of 2021,[6] which includes the roughly 3 million Afghan citizens living as refugees in both Pakistan and Iran
Approximately 46% of the population is under 15 years of age, and 74% of all Afghans live in rural areas.[4] The average woman gives birth to five children during her entire life, the highest fertility rate outside of Africa. About 6.8% of all babies die in child-birth or infancy.[4] The average life expectancy of the nation was reported in 2019 at around 63 years
Afghanistan ranks 210th in GDP per capita at $2474, and that's the purchasing power parity number that takes into account local prices.
Afghanistan was just too big at 39 million people and too poor for "nation building" to work.
Hell, we can't even successfully "nation build" in a smaller country much closer to home like Guatemala in Central America.
Oh, wait, even Guatemala now has 18 MILLION people. Honestly, world demographics are shifting at an astonishing fast pace and I don't think our foreign policy has been keeping up.