Halloween Beginnings
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. Celts believed that on the night before the New Year, the boundary between the worlds of the living and the dead became blurred. On the night of October 31 they celebrated Samhain, when it was believed that the ghosts of the dead returned to earth. To commemorate the event, Druids (Celtic priests) 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.
By 43 A.D., the Roman Empire had conquered the majority of Celtic territory. In the course of the four hundred years that they ruled the Celtic lands, two festivals of Roman origin were combined with the traditional Celtic celebration of Samhain. On May 13, 609 A.D., Pope Boniface IV dedicated the Pantheon in Rome in honor of all Christian martyrs, and the Catholic feast of All Martyrs Day was established in the Western church. Pope Gregory III (731–741) later expanded the festival to include all saints as well as all martyrs, and moved the observance from May 13 to November 1. All Souls Day was celebrated similarly to Samhain, with big bonfires, parades, and dressing up in costumes as saints, angels and devils. The All Saints Day celebration was also called All-hallows or All-hallowmas and the night before it, the traditional night of Samhain in the Celtic religion, began to be called All-hallows Eve and, eventually, Halloween.
Halloween Comes to [North] America
Celebration of Halloween was extremely limited in colonial New England because of the rigid Protestant belief systems there. Halloween was much more common in Maryland and the southern colonies. As the beliefs and customs of different European ethnic groups as well as the American Indians meshed, a distinctly American version of Halloween began to emerge. The first celebrations 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. By the middle of the nineteenth century, annual autumn festivities were common, but Halloween was not yet celebrated everywhere in the country.
In the second half of the nineteenth century, America was flooded with new immigrants. These new immigrants, especially the millions of Irish fleeing Ireland's potato famine of 1846, helped to popularize the celebration of Halloween nationally. Taking from Irish and English traditions, Americans began to dress up in costumes and go house to house asking for food or money, a practice that eventually became today's "trick-or-treat" tradition.
Did You Know?
One quarter of all the candy sold annually in the U.S. is purchased for Halloween. Today, Americans spend an estimated $6 billion annually on Halloween, making it the country's second largest commercial holiday.
http://www.history.com/topics/halloween/history-of-halloween