Yes but Japan also celebrates Halloween, having copied America.

Not much in common with the European tradition of All Hallow's Eve that it originated from.

Just an American thing. Though, things like Trick-or-treating are on the decline sadly so we may just have the Halloween decor and young adult Halloween parties before too long.

Things like being able to go door to door to get candy from strangers are only viable in a high-trust society. America, if anyone can't tell, isn't a high-trust society anymore.

As for why that is, well you have plenty of things to pick from: multicultural/multiethnic society, destruction of the family unit, increased polarization from social media and the corporate press, academics teaching young adults to hate their country and the 'fascists' propping it up. Pick your poison.

Mostly. It spun off of the Irish pagan holiday of Samhain. Then it became All Hallows Eve (night before All Saints' Day)->Hallowe'en>Halloween. From what I understand, it has some presence some other part's of English-speaking world.