How Should Taiwan, Japan, and the United States Cooperate on Defense of Taiwan?
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Have Japan designate one it's islands as New Taiwan. Keep it legally apart of Japan.
Then move every single resident of Taiwan there. Then strip out everything of of value and move it to New Taiwan.
Then the CCP can reunify with a deserted island. Everybody wins. Taiwan and Japan have very close ties so while this is a far flung solution it's better than WW3.
The worst defence would be a military defence of Taiwan. This would probably result in a war with lots of death and destruction and probably Chinese control of Taiwan anyway.
A third alternative would be sabre-rattling and hot air, which will further annoy China, thereby further worsening opportunities for cooperation and give Taiwanese nationalists false hope.