I disagree with your assessment of this subject. Both Korea and Taiwan have had nuclear programs in the past and were ready for nuclear breakout. The US administrations at the time shut down their nuclear programs. Out of these three, only Japan has a population that is thoroughly anti-nuclear. Yet the Japanese population is moving towards the right, and anti-China sentiment is increasing. You should not consider it a hairbrained idea that US allies will remain unarmed while China increases its arsenal.
Then why don't they??
Have you considered that China spends less on military than Taiwan, and South Korea? The fact is China spends next to nothing on its military compared to many other big spenders. The reason why Taiwan and Japan do not pursue militarisation to the level you're hoping is because if they did, China would simply follow suit.
Since you're clearly new to military affairs and relatively ignorant, I'll explain how this works.
Group A understands how much its "adversary" Group B spends on militarisation. Group B understands how much Group A spends. They both have an unspoken "status quo" with regards to militarisation. Whenever either starts spending more, the response is an increase - arms race.
If Japan militarises, it would be the best thing ever for us here since that's exactly what we want to see. China actually militarising. Right now, China is not even trying at all and this is the level of progress we're seeing. Imagine if they actually wanted to militarise. China would overtake the US overall military capability within 10 years. This is my opinion but one I am extremely confident in. Why? Because I
know what Chinese are capable of and it is beyond what even China bulls think. Trust me, China would need no time at all to dominate if they truly saw a need in it. But Chinese leaders know the more they spend on military, the more it invites negative attention and the more it loses out on in developing its people and nation - more important than having military power beyond a certain point of diminishing returns. China wants a military that is absolutely capable of deterring US from military action and any point beyond that yields diminishing returns at the opportunity cost of further development.
Now guess why despite having a ultra right wing government for 20 off years, Japan dares not militarise? Answer (I'll give it to you since you are clearly a newbie to geopol and military) is because Japan is deathly afraid of opening Pandora's box and giving China a reason to militarise and eventually use military. It does not want China to actually start militarising to a point where China's main tool in its toolbox is its ridiculously overpowered military. In such a scenario, China may not stop at simply eroding Japanese influence in the region and actually consider military action on Japan. China is currently 2 Japans and on the path to becoming 10 Japans.
Now is it wise for Japan to pursue an arms race? Which side does an arms race truly benefit?
Now do you know why Japan doesn't and hasn't militarised in the last 20 years despite having the technical abilities and political will to do so?
As for nukes, well China
already has between 300 and 1000 high yield warheads and launches hundreds of ballistic missiles for training
every year. China is not only at a much higher starting position wrt nukes but also accelerating at a pace Japan cannot hope to even try and match even if the political choice is made for that. It's basic maths.
I'd point out the recent interview on Australian ABC news where
Australia would become a target for a nuclear first strike if it went forward with the AUKUS deal. This interview was widely interpreted as a nuclear threat by China among the Australian population, who have now doubled down on anti-China policy and have committed to intervention in Taiwan.
Well any nation that gets nukes or military nuclear tech such as SSN is automatically a nuclear target if it uses nuclear weapons on another nation? Perhaps you didn't know but this is how it has worked since the 1960s across the world.
Example.
If Iran developed and built a SSN and armed that with conventional weapons only but used that SSN to launch conventional attacks on the US, the US may be justified in responding with nuclear weapons. Why? Because nuclear technology is involved in a military conflict.
China state mouthpieces indeed hinted that Australia pursuing nuclear weapons technologies (which an SSN is) would of course invite like with like responses. This like response may not be limited to Chinese SSN using conventional weapons. That's not how any of this works.
Your statement that Japan will get nuked many, many times by China if it intervenes in Taiwan is exactly the reason why the right-wing Japanese military would want second strike nukes. Given Japans fairly large submarine fleet, they would likely opt for a sub-only nuclear deployment, which is by nature a second strike capability. The PLA would not be able to wipe out Japan's submarine fleet in a first strike, whether nukes are used or not, unless the PLAN builds so many nuclear submarines that it can tail all Japanese subs, all the time, even within Japanese territorial waters.
You should read my statement carefully. This is what was written.
"At the moment, in the hypothetical of PRC reunifying militarily with Taiwan, no one is getting nuked or launching nukes BUT if Japan is dumb enough to pursue that program, Japan is not only getting attacked and invaded but nuked, many, many times by China."
Again this is in the case of Japan developing and fielding nukes. If China doesn't actively stop that from happening in the first place, a nuclear armed Japan could only expect to be potentially targeted by Chinese nukes IF a war breaks out between the two. If Japan doesn't have nukes, they certainly would not be nuked. If they had nukes, it's not impossible for China to consider a first strike. The difference between those situations is really Japan having nukes = potentially being nuked vs Japan not having nukes = Japan not being nuked. Very simple stuff.
If you haven't noticed, the US has been pumping out anti-China, pro-Taiwan independence propaganda for more than a year now. Not only for US audiences, we can see from polling numbers that public opinion towards China has started to become very negative in the last few years in the US, Japan, Korea, and Taiwan. You should not underestimate the ability of the US to shape public opinion both within the USA and in US allies. Nobody is better at propaganda. The strategic gain from having a survivable second strike capability is very compelling for deterrence, especially since China it not willing to enter arms control agreements.
For more than a year now? Well no. They've been doing this since PRC began. It's just that Taiwan tensions have gone up a lot since DPP tried forcing hands from both US and PRC with increased flirting with declaring independence through tactics that blur the line. This has resulted in increased attention from all three parties and increased action and media focus.
Your idea that US would encourage Taiwan and Japan to develop and field nukes is absolutely right. It is and would be what US desires. You simply forgot to think about the calculus in Japan and Taiwan, both their civilians and their leadership. Japanese civilians and leaders do not want to become potential nuclear targets for no reason. They have zero risk of being nuked by China if they don't field nukes. They have non-zero risk of being nuked by China if they develop nukes. Surely you can comprehend this simple concept. This is why Japan will not field nukes.
In fact Japan fielding nukes is so impossible that Japan hasn't even discussed militarising yet amongst itself! The escalation ladder in that regard goes like this.
Level 1. Japanese leaders consider militarising Japan
Level 2. Japanese citizens decide whether it is appropriate to militarise Japan
Level 3. The decision is made to militarise Japan
Level 4. Japanese leaders consider developing and fielding nukes
Level 5. Japanese citizens decide whether it is appropriate to have a nuclear armed Japan (hence being a nuclear target by the world's second most militarily powerful nation which happens to be next door and one soon to have over a thousand nuclear warheads).
Level 6. The decision is made to have a nuclear armed Japan
Level 7. Nuclear buildup.
At the moment we are at Level 0... while Japan already has a deeply right wing and anti-China government for the last 20 odd years and depending how to define it, anti-China governments for the last 70 odd years.
So why have they never left Level 0? Honestly ask yourself.
Could it be because they
know they are not only militarily WELL behind China now but also that they have no hope of out-accelerating China while China is only running at 30% potential and Japan running at 90% potential? They know if they militarise and go at 100%, China could simply run at 50% and dominate even further.
The nuclear analogy is like this. China is the group in a gun store with 5 machine gun armed guys with their weapons hovering around Japan, 2 guys armed with some child proof scissors. And you are saying these two guys could and should start very slowly and obvious go reaching for some pump action shotguns and load those weapons all the while shouting loudly about a desire to kill the 5 guys. Not very smart is it even if they are encouraged to.
Japanese leaders and people are not perfectly willing to become nuclear targets for no reason at all.