@tphuang
And if we look to future, we can expect the Chinese stock of advanced weapons to roughly double in the next 9-10 years. That's based on historical GDP figures, % spent on the military, along with assumptions on a 30-year typical weapon lifespan and constant % spent on procurement. But what will this be spent on?
If we look at the situation today, the key to a successful US military intervention over Taiwan is Japan and Guam. Guam is US territory, but Japan can be peeled off.
At the moment Japan is committed to supporting the US in a Taiwan. But Japan can be persuaded not to allow the US military to use Japanese bases, because Japan is essentially a larger version of Taiwan, which China can blockade.
Both Japan and Taiwan are densely populated islands with no natural resources and rely on imports for food and fuel.
Geographically, they both lie on the fringes of the Asian mainland, relatively close to China. In comparison, the US is all the way across the vast Pacific Ocean. There are only a few scattered islands in the middle that could be used to support Taiwan, Japan or Guam.
So if China wanted the capability to conduct a surprise first missile strike and then deny Japan electricity, fuel and food (like Taiwan), it's feasible for China to build such a force
If China wanted to conduct a Taiwan-style missile strike on Japan, I reckon something like 500 DF-17 MRBMs with a reload of another 500 DF-17 should have a similar effect and ground the Japanese Air Force. This should be easily affordable given a DF-17 missile cost of <$2 million.
That opens the door to follow-on airstrikes by the Chinese Air Force. However, Japan is at a significantly further distance than Taiwan and there are many fewer Chinese airbases in range of Japan, plus there is a thin strip of North Korean territory in the way if Chinese fighter aircraft want to reach Central or Eastern Japan. Otherwise these areas will become secure rear bases.
In terms of Chinese access through North Korean airspace, I don't see a big issue. North Korea is internationally isolated and depends on China for 80-90% of its trade. And if China loses a war with the US, then North Korea is utterly alone and faces the prospect of collapse. But if China wins a war against the US, then the US military threat from South Korea is gone. So North Korea will tacitly allow Chinese aircraft through its airspace.
Now, Japan is still quite a distance with the Westernmost point of the Japanese Home Islands some 900 km from Shanghai. The distances are a little further from Chinese Manchuria to the rest of the Japanese Home Islands.
I reckon China would still need to sustain at least 400 fighter-sized sorties per day to prevent Japanese airfields and ports from being resupplied by the US.
So in terms of procurement, that means more J-20 stealth fighters, J-16 strike fighters, Y-20U tankers and also H-6/H-20 bombers. This would also also require additional bases in Manchuria
If China pursues this military strategy against Japan, I don't see any effective counter that the US or Japan could do.
In such a scenario, Japan can add very little to a Taiwan conflict, so what is the point in Japan committing national suicide by joining the US in a way against China?
At the same time, from the US perspective, Japan could become a huge liability as all of Japan would be under sustained air attack, yet cargo ships and cargo aircraft still have to land in Japan to break a blockade.
So I expect that in 10 years or so, both the US and Japan will agree that it isn't in their interests for Japan to go to war against China over Taiwan. And it's not credible for the US to succeed in Taiwan if the nearest bases are in Hawaii or Australia.
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Now, this is my best guess as to what will happen in the future, assuming we avoid a war. But it's even more probable if there was a war tomorrow. In the aftermath, China would likely rebuild everything within 5 years, given what we've seen happen in past wars and the speed of China's peacetime construction. Then I reckon it would take another at most another 10 years for China to conduct the same strategy against Japan and Taiwan if necessary. In the following 10 years, the military balance would be overwhelmingly in China's favour.
Hence my view that it would be stupid for Japan to join the US in a war against China.
South Korea and SE Asia have already come to the conclusion that is better to be neutral than follow the US
