north korea...from tumbling satellites to city killing ICBMs with no r&d

No R&D

Hardly any flights tests and certainly none that prove ICBM capability. Not even close. US had vast regions to test theirs and vast reservoirs of cash to pour into the effort.

Barely able to cobble together a few kilotons and ever those were questionable and thought by many to be hoaxed by exploding huge piles of conventional explosive underground to simulate nuke testing for the seismos.

Certainly nothing of the megaton range that "miniaturization" suggests.

and again, to get their the US and every other nation that has done it did so with far greater resources than NK ever had.

If they have it it was given to them either by China, Russia, Israel, Pakistan or the US.