In 1582 people realized that there wasn't enough days in a year, so Pope Gregory XIII made us change from the Julian calender to the Gregorian calender. April fools is celebrated because some people didn't know so they still celebrated (new year) in April. However of years the concept of April Fools has changed.
Retared: WOOOOO! APRIL FIRST HAPPY NEW YEAR!
Douchebag: What an April Fool.
GUY: So many April Fools