The History Of Halloween

Halloween started as a Celtic Festival of Samhain.  It is a period shrowded in mystery as days start to get shorter.  It was the end of the harvest season.  People would wear masks and costumes, and light big bonfires to ward off ghosts.  In the 8th century, the pope declared Nov. 1 to be all saints or martyrs day.  Eventually this day became know as All-hallowmas, and the night before as All-hallows eve or Halloween.  It was felt the Church supported these holidays to supplant the Celtic Holidays. 
In the United States, Halloween was not generally celebrated.  However in the 19th century, with immigration from Ireland and other areas, this holiday was carried to the United States.  In the early 1900s the holiday was changed to become more a family oriented celebration.  Vandalism and tricking which was a part of the holiday began to disappear. 
One other interesting aspect of old Halloween was the idea that this night you were closer to the spirits, and consequently they could help guide you.  Many women used this night to try and determine who their future husband might be.
http://www.history.com/topics/halloween
This few notes are taken from History.com.