Comment by throwawayffffas

Modern weapons use plutonium not uranium, uranium weapons can be constructed.

All it takes is the enrichment to produce the fissile material for a weapon.

As far as I know countries have agreed to not build weapons, with the exception of those that already have them, there is an international body that monitors enrichment sites, but checks are voluntary a country can choose to not accept inspections and/or build additional secret enrichment sites.

The fissile material is not sufficient for a weapon though, as I understand there is quite a bit of science that goes into making a bomb.

Additionally, first generation weapons are large and unwieldy, i.e it takes a bomber to deploy a single weapon with a very small yield.

Miniaturization, building a weapon small and light enough to put on a missile is a significant problem that took the current powers years to get over.

But that's about it, if you can figure out how to make a small bomb of variable yield, you can make bombs small enough to fit a large backpack, and thermonuclear weapons that fit in a ballistic missile as well.