https://en.wikipedia.org/wiki/Territorial_disputes_in_the_South_China_SeaThis is the powder keg. Depends how hard China wants to go to achieve its complete borders, which includes Taiwan and the South China Sea.
Ideally it will stay regional if it happens. If it goes global expect to see China, Russia, Turkey, North Korea, and Pakistan align together. US, of course fucking Australia, Japan, South Korea, India, NZ, and ofc Britain. Iran is a total wildcard. The Baltic States would be wise to join on behalf of the Americans because they have the most at stake (Besides South Korea).
Would be kinda new for us Yuroscum to get to sit back and watch a major war happen for once, popcorn on the side.