The 2030s is much more speculative, but we can make a reasonable guess as to the military balance in 2030.
We can see that the Chinese Air Force and Navy are procuring more big-ticket platforms that the US is.
So we can reasonably assume Chinese procurement of munitions and other systems will be comparable, given these tend to be a lot less expensive.
So here's my guess on the 2030 Chinese military
Air Force
1000 J-20. Based on 100+ annually, as per Patchwork and observed serial numbers
600 Flanker airframes (J-11/J-15/J-16)
600 J-10 airframes
400+ H-6 and JH-7 strike aircraft
100+ Y-20U tankers. There are about 20 Y-20 airframes produced annually.
Munitions and Missiles
We can see that the US plans on buying the following in the next 6 years
a) 4000 JASSM missiles
b) 700 HIMARS launch trucks
c) 106K GMLRS missiles @ $220K each
a) The Chinese equivalent to the JAASM is the DF-17, which is comparable in range and cost
So let's say China buys just 2000 DF-17, which is only half the US plan of 4000 missiles
b) Those DF-17 would be launched from 500 Launch Trucks, in comparison to the 700 HIMARS the US is buying
c) China doesn't need 100K GMLRS as these are expensive short range missiles for a ground war.
Instead, they could buy low-cost munitions like 100K JDAM glide bombs and another 100K Shaheed-136 piston-engine powered cruise missiles. This would only come to $4 Billion, which is only a quarter of what the US is spending on GMLRS
Then if you look at the geography of the Western Pacific, all of Japan is within 1300km of the Chinese mainland. That would be within range of the DF-17, Shaheed, J-20 and also the Flanker airframes. There are also 150+ airbases in China versus approx 10 in Japan. So when you look at Chinese military capabilities, you have the recipe for outright Chinese air superiority over Japan.
Japan can then be blockaded by air and sea indefinitely. In addition, you could allocate say 100K munitions for targets in Japan. Japan is a small but densely populated island which has to import all of its natural resources, including 30% of its food. In comparison, China is the same size as the continental USA and shares land borders with many countries for trade, so China can be broadly self-sufficient. So we can see Japan would collapse in weeks/months in a modern-day version of Operation Starvation. This scenario still applies even if the US military gets involved.
We can extend this scenario to South Korea and Philippines (if required), as there is more than enough spare Chinese military capability.
As for Taiwan, they already face this strategic situation today
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There's very little that the US can do in this scenario, as the US will be reliant on a small number of submarines, carriers and bombers operating from a handful of distant bases in the 2nd Island Chain and beyond. And those few bases would be under intermittent attack.
This still applies even if they US starts fielding larger numbers of submarines, NGAD, long-range stealth bombers or long-range hypersonic missiles for example after 2030.
From 2030-2040, we could see China buy another 1000 J-20s and its NGAD successor for example. And if NGAD really does have long range, then we could see Chinese NGAD conducting air-superiority operations deep in the Pacific and over Guam for example. There are other Chinese military capabilities as well. By 2040, I would expect a minimum of 6 Chinese carriers and a maximum of 10 carriers if relations with the USA are bad.
@BoraTas
Yes, talk of a "decade of concern" doesn't really make sense.
1. At the granular level, the analysis above goes into some detail as to what is happening
2. At a medium level, if you model the "stockpile" of annual weapons procurement and assume a typical 30 year service life, you can see the Chinese stockpile doubling by 2030 and then increasing another 50% from 2030-2035. In comparison, the US is pretty much flat.
3. At a high-level, you get into how China already has a larger economy than the US in terms of actual output when measured by PPP. Furthermore China should continue to grow faster, which will support even more military spending. And from a requirements perspective, historically the world's largest trading nation builds the largest Navy to protect its global trade interests and investments.
So we are looking at US military superiority dropping away every year for the next 20+ years, just on the current size of the Chinese economy and current military spending levels.
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So what does this mean?
For Japan, the way out of this security dilemma is good relations with China. It is pointless for Japan to have an alliance with a distant USA that can provide neither military security nor economic prosperity. A similar calculation applies to many other countries in Asia.
For the USA, they have to publicly acknowledge that a war with China is not an option. Otherwise we'll see a larger and faster Chinese military buildup to "persuade" the USA.
