Approximately 2,000 years ago, the ancient Celts, who lived in what is now the United Kingdom, Ireland and northern France, marked the start of the new year on November 1. This was the time when the harvest ended and the winter months began. They believed that the night before the new year was a time when the boundary that separated the living and the dead opened and ghosts returned. The spirits helped the Celtic priests, called druids, predict the future. This was celebrated as the festival of Samhain. The Celts wore costumes, told fortunes, built bonfires and sacrificed animals to welcome the spirits. At the end of the celebration, they used the sacred bonfires to light their hearths for the upcoming winter.
When the Romans conquered the Celts in 43 A.D., they merged two Roman festivals with Samhain: Feralia remembered the passing of the dead to the next world, and the festival of Pomona celebrated the goddess of fruit. As Christianity spread throughout the region, the pagan traditions evolved into All Hallows' Eve, the evening before the Christian All Souls' Day, established to honor the dead.
During the early Colonial period, Halloween was downplayed in the northern colonies due to the strong influence of the Puritans, who did not approve of the pagan origins of the holiday. In the southern colonies, it was celebrated more as a harvest festival. Colonists heard fortunes, told stories, sang and danced in celebration of autumn.
As Scottish and Irish immigrants arrived in the 1800s, Halloween became more popular in the United States. They brought with them the tradition of dressing up in costumes to go trick-or-treating, and people would go from house to house asking for money or food. Wearing costumes dates back to the Celts, who believed that dressing in costumes would fool the visiting ghosts into thinking they were fellow spirits. Trick-or-treating may come from early All Souls’ Day parades where the citizens gave the poor "soul cakes" in return for a promise to pray for their dead.
In time, Americans removed the superstitions and pranks from the holiday and focused more on community parties and family get-togethers. By the end of the 19th century, most Americans were celebrating Halloween.
Up until the mid-20th century, Halloween was community holiday, where towns held parades and parties. Trick-or-treating became popular again and families handed out candy to avoid being "tricked." Vandalism became an issue during this time and that, combined with the baby boom of the 1950s, turned Halloween into primarily a holiday for children.
Halloween in the 21st century is one of the most popular holidays in the U.S. As of 2017, Americans spend an estimated six billion dollars each year on the holiday. Dressing up in costumes is a popular activity among children and adults. Children still go trick-or-treating, and many towns hold trick-or-treating events in malls or schools.