California is the one border state that…
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Is the most populated
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The most overrun
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The most disarmed
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The most defiant to the US government
5 The hub of the entertainment world (propaganda).
If any border state became a flash point, I think it's the most likely by far. The government there is very corrupt, it's home to a lot of big fish in this game, the people can not fight back as effectively, MS13 and other gangs are rampant, and taking control back from them without serious destruction and chaos would be very challenging given its size, population, and mass urban zones.