I used to be an obnoxious gun control advocate until I learned that California's gun control legislation was brought about in response to the Black Panther's patrolling predominantly black neighborhoods while armed to protect the people of the neighborhood from state sponsored (police) violence.
Reference to start from: https://www.kcra.com/article/liberty-limits-black-panther-pa...
This topic is full of subtlty so recommend reading the sources from that article and so on.
Were they what precipitated it or were they one of the many factors used to get the public on board?
9/11 didn't write the patriot act.
and china. police in china generally is not armed. (china may or may not be considered a developed country, but i think that distinction is irrelevant. i am pretty sure there are more than three countries in the word where police is not armed, or where armed police is a distinct unit used only for specific tasks where arms are needed). but that wasn't the point i was making, rather, in most countries police simply does not get violent, nor do they have to fear being shot at, because of gun controls.