The original Halloween was actually an ancient Celtic festival of Samhain. The Celts, were around about 2,000 years ago and lived in the area that is now Ireland, the United Kingdom and northern France. Their new year was celebrated on November 1st. 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. Celts believed that on the night before the new year, the boundary between the worlds of the living and the dead became very thin.
On the night of October 31 they celebrated Samhain, when it was believed that the ghosts of the dead returned to earth. In addition to causing trouble and damaging crops, Celts thought that the presence of the otherworldly spirits made it easier for the Druids, or Celtic priests, to make predictions about the future. At that time, these predictions were very important. Life was a fragile thing and any help was huge.
To commemorate the event, Druids built huge sacred bonfires, where the people gathered to burn crops and animals as sacrifices to the Celtic deities. During the celebration, the Celts wore costumes, typically consisting of animal heads and skins, and attempted to tell each other's fortunes. When the celebration was over, they re-lit their hearth fires, which they had extinguished earlier that evening, from the sacred bonfire to help protect them during the coming winter.
Originally, the Irish hollowed out turnips and put scary faces on them to scare away evil spirits. During the Great Potato Famine, many Irish were forced to leave Ireland and come to the United States. Turnips weren't as easy to come by, so the Irish turned to pumpkins instead.
Before the early 1900's, the only people celebrating Halloween were the Irish and Scottish. Most Americans weren't too interested in going to neighbors and asking for treats.
The first Americans brought their traditions to the US and mixed theirs with the Native Americans. This turned into festivals celebrating the harvest. They would tell ghost stories and tell each others futures, dance, sing and give God thanks for that years blessings. Of course some areas this was still frowned upon by the Puritans.
The pagan Celts believed that after death, all souls went into the crone's cauldron, which symbolized the Earth mother's womb. There, the souls awaited reincarnation, as the goddess' stirring allowed for new souls to enter the cauldron and old souls to be reborn. That image of the cauldron of life has now been replaced by the steaming, bubbling, ominous brew of a witches' cauldron.