Halloween's origins date back to the ancient Celtic festival of Samhain (pronounced sow-in). The Celts, who lived 2,000 years ago in the area that is now Ireland, the United Kingdom and northern France, celebrated their new year on November 1. This day marked the end of summer and the harvest and the beginning of the dark, cold winter, a time of year that was often associated with human death.
The first Halloween celebrations [in America] included "play parties," public events held to celebrate the harvest, where neighbors would share stories of the dead, tell each other's fortunes, dance and sing. Colonial Halloween festivities also featured the telling of ghost stories and mischief-making of all kinds.
In the late 1800s, there was a move in America to mold Halloween into a holiday more about community and neighborly get-togethers than about ghosts, pranks and witchcraft. Parties focused on games, foods of the season and festive costumes. Parents were encouraged by newspapers and community leaders to take anything "frightening" or "grotesque" out of Halloween celebrations.
http://www.history.com/topics/halloween