It took the US 18 years to realize that confessions obtained under torture are null and void?

No, that part took a couple months, a year at the very most.

What took 18 years was getting anyone with influence over the US military to acknowledge the obvious.

If the US is ever to become a nation of basic human and civil rights for all and rule of law it needs to be reworked from the ground up.

Yup! It’s long past time to stop trying to fit a diverse and modern society into the notions of a bunch of rich white slave owners.