Why does the US get to continue uranium enrichment/building of nuclear warheads, but places like Iran are not allowed to do so? 1. The US doesn't build nuclear

Why does the US get to continue uranium enrichment/building of nuclear warheads, but places like Iran are not allowed to do so? 1. The US doesn't build nuclear warheads, and presently doesn't have the capability of replacing the ones it has. This is a whole issue of its own. 2. Because of the Treaty on the Non-Proliferation of Nuclear Weapons, which Iran ratified.