>Hallowe'en isn't an American holiday. It combines medieval Christian All Saints with a far more ancient Celtic festival of Samhein.

Yes. Which is very popularly celebrated in its current form in the USA and is being (to some degree) also being celebrated around the world as a result of American cultural exports.

Halloween as the majority of the world knows it is an American holiday. Other countries that have (some form of) Halloween celebrations are not doing it due to Irish influence or something.

Also, Dia de los muertos is NOT a really big thing in Mexico. It's popularity increased after the 007 movie in Mexico City, and even then there's only a single town/city that has always celebrated rather than the entire country. I think it was the media that made it like it was celebrated by all Mexico which is not

Well first and most importantly, I'm not sure how to take your argument as I never made any statement one way or another on what seemingly seems to be a rebuttal using a negative as a form of correction.

It's a western Christian holiday and the US is largely a country settled by western Christians in the early days, so most of the US follows the holiday. That makes it an American holiday in my book, although the US is by far not the only ones that follow it or the origin of the holiday.

The US has put its own spin on how the holiday is celebrated and spread those customs to other parts of the world too, so the topic is a bit less white or black in that there is a two-way spread of cultural customs.