Don’t think I agree. Took the U.S. 7 years after Fat Man to develop a true H-bomb employing Teller-Ulam configuration.
What N. Korea is almost certainly talking about is a fusion-boosted weapon in which tritium is injected onto the pit immediately before implosion. The result is a small amount of fusion. But the main purpose is to increase the neutron flux to improve fission efficiency of the primary. The vast majority of the weapon yield is still due to fission not fusion. In contrast, for a two-stage Teller-Ulam bomb, roughly 90% of energy is due to fusion of secondary.
Once they knew in could be done, the Soviets, Brits, Chinese took only 3-5 years to go from fission to two stage fusion. The French took 8, but for the first 4 they were on the totally wrong track.
Admittedly the Indians took 24 years, and the Pakistanis are taking a similar time - But Kim should be able to beat that.
Remember that we had to discover that design principle. The Norkies can read about it on the Internet.
I think Mr. Kim disproved those theories overnight!
He has done everything he said he was going to do, and he has said we will use his (proven) missiles with his (now proven) fusion warheads to destroy the US.
He kills relatives by shooting anti-aircraft guns and mortars at them. He also loves to turn starving dogs loose on them.
Why would we expect him to stop now?