Why would it be unpleasant for us?
Because we will lose our trading partners and allies for 1/2 the Earth which will be an enormous economic loss, plus our security situation will be perilous as we are a Pacific nation, plus our allies would become potential enemies. Little countries like Japan, Taiwan, South Korea, etc.
And as for let them defend themselves, it’s America I’m worried about. It is better to fight the Chinese there than here. For us.
Why would it be unpleasant for us?
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because the military would gain the upper hand in china.
Their current ambitions go far beyond the south china sea.