North Korea is known to be one of the most secretive societies in the world.
If they had something that made them able to inflict so much harm on their neighbors, they wouldn't be quiet about that. They'd boast.
Its one thing to trot out a really cool looking aircraft and call it "stealth" but is it really? Stealth requires more than just the form of the aircraft but advanced composite design which I do not believe China or Russia have the capabilities of constructing
American YF-22 and YF-23 prototypes flew with a new type of stealth skin material in 1990. The older type (which is effective but was replaced because it's more work to maintain) flew on B-2s in 1989 and YF-117s in 1981. The elapsed time between any of those dates and now is how many years behind the USA another country could lag and still have found an effective material to make a stealth plane's skin out of by now. (And people have been caught trying to sneak technical details of these planes' development out to other countries.)
nor do they have the advanced avionics and software to fly the plane with confidence.
I don't want to be offensive or personal about this, but that idea is just silly. Both countries have been independently developing, producing, and flying their own combat planes for decades. Even if they lag behind North American & European countries in some technicalities, their ability to make the planes work is soundly proven beyond any doubt. To suggest otherwise is like that scene in "Bridge on the River Kwai" where the captors demand help from their captives in designing a bridge, in a region where people have been building bridges for millennia. For that matter, flight control in planes built for maneuvering not only isn't a great weakness in the major Asian powers' planes, it's pretty much their greatest strength.
Russia can seriously be said to be more advanced than the USA in terms of aerodynamics & flight controls. Their planes have long been more maneuverable than our nearest counterparts (including with the comparison between F-22 and T-50) without any greater tendency to fall out of control. They have a history of advanced experimentation and rapid readiness for mass production of complex concepts in aerodynamics that the USA never even tried or only briefly tinkered with and dropped. Neither of Russia's two main producers of fighters has made one without thrust vectoring since the 1990s (several years before F-22 production began, and we've still put out another new design since then without it), and their systems can redirect the thrust not only up or down, in some cases to a wider range of angles than an F-22, but also sideways, and independently in two different directions in the same plane's right and left engines. They've also put canards for maneuverability (including in combination with tail fins rather than replacing them) on some production planes even longer than that (on and off), while the USA had just a few experiments with the idea (by NASA instead of the Air Force) and never went anywhere with it. One Russian company recently built and flew an innovative and unprecedentedly maneuverable prototype with forward-swept wings that could have gone into production by now if it had found a buyer, and the aerodynamic experience they gained from that influenced part of the electronic control systems they've used in two other non-forward-swept models they've released since then.
China hasn't been recognized worldwide as quite such a leader in aerodynamics & maneuvering as Russia has, but their own planes have generally kept up in worldwide context, and they have Russian planes and have bought some of the Russians' research & development data. The configuration of the J-20 is a delta wing with canards in front (pretty standard on all of the latest European fighters), which is a complicated thing to control, but they've done it before on the J-9 and J-10, so the Chinese have been quite familiar with its quirks and the appropriate fly-by-wire programming to deal with it for years, just like the Europeans (more so than Americans, since Americans haven't worked directly with anything in that configuration). By using that configuration on the J-20, they're sticking with what they already know they can do, not taking a risk with something that would be odd and new for them.
The other issue of course is that should war break out between the North and South, can the USA afford to be engaged in another protracted war?
And if we can afford it, do we have the will to do it?
