The ancient Celtic Pagans would celebrate Samhain, which was a 3-day event to celebrate deceased loved ones and their Gods and spirits.
They would have a 3 day Fire festival where people would secretly play pranks and tricks telling others it must have been the ghost and their Gods.
Later the Roman Catholics would do a similar celebration but they replaced the Gods with Christian Saints and martyrs.
They would pray and some still celebrate All Saints Day to this day. It's November 1st.
So the Irish settlers In the 1800's started a similar Holiday called Halloween. And they would give treats out to kids in an attempt to prevent them from wanting to do pranks. This is when Trick-or-Treat was born.
Costumes became a way to dress up for kids to pretend they were goblins and would terrorize the neighborhood if they weren't “paid off”... with treats🤣.
In the 1920s costumes became available to buy rather than having to make one.
And the candy industry jumped on the bandwagon during the economic boom after WWI

Halloween is estimated to be at least 7+ billion dollar industry and a huge part of most of our lives.
Here's my Goofy family...aka the best treat of the night ❤️.
❤️❤️❤️ She was dead Elsa❤️❤️❤️