Apparently, America played a big role in HK riot this year, and the years of past. Now Trump brazenly passed the US "domestic" law to reinforce the rebels in the island, (Though actually the "law" is not worth the paper it is printer on.); well, if this can be tolerated, what elses cannot?
China Mainland has done something to counterattack such a rude interference in her internal affairs. Attached below is her reaction, and why does she opt for such measures.