According to History.com, the tradition of Halloween dates all the way back to the ancient Celtic festival called SamhainSamhain

Druids were Celtic priests who constructed sacred bonfires where people gathered to burn crops and animals to the Celtic deities. The Celts wore costumes consisting of animal heads and skins and they attempted to tell each other's fortunes.

In the 1800s

During the middle of the nineteenth century autumn festivities were common, but Halloween was not celebrated everywhere in the United States. By the second half of the nineteenth century, America was full of immigrants from all countries. Having so many different backgrounds of people helped shape the holiday of Halloween as Americans began to dress up in costumes. It has been said that wearing a costume would help one to go unnoticed by ghosts. People would wear masks, and leave their homes so the ghosts would assume them as fellow spirits. Along with leaving their homes, they would go house to house to ask for food or money. This began the early idea of Trick-or-Treating.

Halloween parties became popular for both children and adults. The parties focused on games and festive costumes, but several guardians at the time were told to take anything frightening out of Halloween celebrations. Due to this Halloween lost most of its superstitious and religious implications in the twentieth century.

By the 1950s

For more information about the History of Halloween please visit: http://www.history.com/topics/halloween