Some believe the Celts celebrated Samhain because they thought that the boundary between the worlds of the living and the dead became blurred on the night of October 31. Therefore, they celebrated by lighting bonfires, wearing costumes and masks (often consisting of animal heads and skins) to disguise themselves so that the ghosts of the dead could not recognize them. They would also leave food and offerings out for the ghosts so they would not steal or damage their crops.
Later in history, the Catholic church moved All Saint’s Day to November 1. This holiday was originally an ancient Celtic holiday in honor of the dead, and later on, it was influenced by the Christian celebration of All Souls’ Day, which commemorates the souls of the dead who have not yet reached Heaven.
In colonial America the original Halloween customs were not observed. It was only after a large influx of Irish immigrants to the country in the 19th century that these traditions began to be practiced with enthusiasm in parts of America.