Why do children demand “trick or treat” during Halloween?

When the Irish introduced Halloween to America, children celebrated with a night of mild vandalism. Their bag of “tricks” included breaking or soaping windows or overturning outdoor toilets. Soon they realized that adults would offer candy or other “treats” to stop these tricks. They then offered the homeowner a choice of giving them goodies or suffering the consequences. This mild blackmail demand came as, “Trick or treat?”