Halloween originated from the ancient Celtic festival called Samhain, which marked the end of the harvest season and the beginning of winter. It was believed that on this day, the boundary between the living world and the dead was blurred, allowing the souls of the dead to return to their homes. To ward off these spirits, people lit bonfires and wore costumes. Later, the Christian church established All Saints' Day on November 1, with the evening before called All Hallows' Eve, eventually shortened to Halloween. This was partly an effort to Christianize the pagan festival of Samhain. Over time, Halloween evolved from a religious observance into a more secular, fun holiday involving customs like trick-or-treating, costume parties, and pumpkin carving. These traditions were brought to America mainly by Irish and Scottish immigrants in the 19th century and spread globally by the late 20th century. Today, Halloween is widely celebrated as a festive day for spooky fun, dressing up, and treats.