After World War I broke out, America pretty much "lost it's innocence and began to grow up". The mentalities of Halloween and other such holidays were skewed, and stopped being celebrated by adults, thus it became a children's holiday. It became a popular tradition for kids to roam the streets at night, but as they did so it began a resurgence of the dark side that had demeaned the holiday in the past. Thus it became known as "Mischief Night."
In the years following WWI, there were many acts of vandalism during the night of Halloween. One year, in 1930s New York, kids broke an estimated 1000 windows in the Queens borough. It wasn't uncommon that the pranks would sometimes be deadly. So, some towns tried different methods to quell the beast. One such town is Anoka Minnesota, who decided it would be a good idea to hold the first American parade/festival on the night of Halloween. It was a success for the most part.
But again, WWII broke out and many Halloween festivals were ignored. Many kids disregarded Halloween at that time, putting most of their time and energy into the war effort (i.e. food or metal scraps). But, after the second great war, came an extreme resurgence in Halloween. Post WWII America, there was a baby boom and such a boom also happened with the Halloween holiday.
To make sure kids went home on time (primarily to avoid vandalism), radio stations would hold prizes to all kids who could get home within 30 minutes of the broadcast. Events like organized trick-or-treating helped subdue Halloween's more mischievous side.
But in 1970s Detroit, this night soon became known as "Devil's Night", as many houses were lit up in flame as simple, but deadly pranks. People began fearing for their lives and the lives of their children and their homes on Halloween. Rumors began to spread that kids were dying because of trick-or-treating because of razor-blades and poison in the treats. And although it was true that razor-blades were found pushed inside apples and poison was found often in candy, many police investigations realized that these were, nine out of ten times, domestic attacks within the family. Still, many parents began accompanying their children in trick-or-treating.
Today, many modern day Neopagans and Wiccans consider Halloween one of their most sacred nights of the year, believing like their Celtic ancestors, that the veil is thinner on this night. Unlike their Celtic ancestors though, they instead invite these dead loved ones and spirits bak from the grave.
Americans today spend a rough estimate of $2.5 billion a year on Halloween, making it the second most expensive holiday. More than half of all homes get decorated, and most kids trick-or-treat. Many dress-up, it's a popular custom to bob for apples, to tell ghost stories and to put faces on pumpkins. Now you know why. Although the past few decades have turned Halloween into a primarily childish holiday, it isn't uncommon for adults to celebrate it now too.
And that's the origin of Halloween. But wait... what ever will I do for the seventh part tomorrow?