Assassinate local leaders. Destroy infrastructure. Set wildfires. Use your imagination.
If you have 20k+ operatives in a foreign country (especially a country with freedom-of-movement like the US), and you could activate them, either all at once, or in echelons, what would you have them do?
Supposedly, the Soviets had plans like this in place for the US, during the Cold War. The Americans (a fictional TV series based on real-life events) had an episode on this very scenario, a while back.
It wouldn't surprise me if other countries had similar sleeper agents here in the US. Probably the Russians still do.
One thousand Chinese (or any nationality, for that matter) spread across America, each with a book of matches, could ignite unimaginable destruction nationwide in just one night. Tens of thousands, that much more.
>Assassinate local leaders. Destroy infrastructure. Set wildfires. Use your imagination.
They would have to do it in the first day. By sundown anyone that looks remotely from China would be gunned down or arrested.