Halloween is an ancient holiday and my personal favorite one of them all. It began from Celtic and Gaelic harvest festivals.
Interesting, I did not know that!  Did they dress up in costumes back then as well?
Dressing up began around the time of a holiday called Allhallowtide which was intended for morning the dead such as saints and all the faithfully departed. Crazy huh?
Sort of like Dia de los Muertes, right?  That is neat!  Are there people who celebrate the original meaning of Halloween?
Yes although Day of the Dead is a mexican holiday but it is acknowledged in many cultures. 
It is fascinating that the holiday seems to cross so many different cultures but has a similar premise.  Have American's always celebrate Halloween?
It is possible, I feel the tradition of trick or treating, pumpkin carving and haunted attractions began here in America
That makes sense.  It is all about the candy and costumes these days.  Do you celebrate Halloween?