Sometimes you do not get to choose...sometomes your are forced to play.
THiose who believe that South Korea would stand by while the US and JApan fought for their lives are, IMHO, sorely underestimating the SKOR mind set.
They are and have been solid allies for decades...and I believe if it came down to it, they would stanf by that alliance.
Like Kwaig, I pray we never have to find out...but as I say, and as we have found in the past...somtimes you are not left with a choice.
As it is, US, JMSDF, ROKN, and the RAN together are a very powerfu...and for the forseeable future, an allied force that is not about to be overpowered at this stage.
With current projections, particularly if the US continues to turn things around...I do not believe it would ever become wise for either side to test that.
But, others have, in the past, done so. I pray that it does not occur again...but I also pray that we will not forget the hard lessons that that type of peace is best preserved through strength.
Time will tell...and I really expect, with my own health, and also be cause I honestly believe God in Heaven has other plans...that it does not happen at all.
Alliances can and are broken when it is no longer in the interests of both parties. That is simply part of the historical record.
Plus Japan/USA would NOT be fighting for their lives in a hypothetical war against China. The continental USA is safe on the other side of the Pacific Ocean, and the Japanese Home Islands are far away enough from China that Japan could mount continued resistance and couldn't be conquered with an amphibious invasion.
Also note that South Korean politicians and the general population have a very different view of going to war with China, than the military does.
---
The USA would be glad that South Korea doesn't join in a war against China.
Because if it does, we will likely see the US Army trying to fight the entire Chinese Army on the Korean peninsula, where the US has to throw away its air-sea advantage, and engage the Chinese army at close range.
But as you say, sometimes you have no choice.
Suppose Fatty Kim decides to start a war against South Korea, whilst China and the USA were fighting. China would have no choice but to join that war, because the alternative is that North Korea is defeated and US troops will be poised to cross the Yalu river into Mainland China.
And in a long war, who is more likely to win?
---
In the past, remember that the USA completely outclassed both Imperial Japan and Nazi Germany in terms of population and economic/industrial heft.
That is most certainly not the case with China, which has 4x the population and therefore the economic potential of 4x USA.
Note that over the past 15 years, China's R&D spending grown to 2.1% of GDP. This level of R&D spending is exceptional, as it is twice as high as any other developing or middle-income country. This R&D spending level places China firmly amongst other wealthy hi-tech nations, and note Chinese R&D spending is still ramping upwards.
With the recent trade war, we can see the US has finally come to this realisation, whilst South Korea came to this conclusion many years ago.
But it is unlikely that China will deliberately start a war, as China knows that a wealthy hi-tech China would have so much economic/military influence that it can get what it wants without a war.
