Halloween is not an American invention, it was not introduced by service bases. It has long since been a Scottish tradition which would have been exported to the States. The "trick or treat" part is the only US addition. Scots children would tradionally dress as up and go around their neighbours "guising". They were rewarded with fruit, sweeties or a penny in exchange for doing a wee turn, telling a joke, singing a song etc. "All Hallow's Eve" is supposedly the most magical night of the year, the dressing up, as far as I remember, was in order to scare of the witches and evil spirits which came out on that night...As a child growing up in Scotland in the sixties, this was one of the highlights of the year, on a par with birthdays and Christmas.