On this day in 1572: The Dutch War for Independence from Spain began.
On this day in 1582, Pope Gregory XIII adopted the Gregorian Calendar. That meant New Year's Day moved from the end of March to January 1st. The change was widely publicized, but some people didn't get the memo, and others just didn't want to go by the new calendar, so they continued to ring in the New Year at the end of March. Some say that was the origin of April Fool’s Day as those who didn't make the change were called April Fools.
On this day in 1924: Adolf Hitler was sentenced by a court to five years in jail for high treason. He was released on Dec. 20.
On this day in 1984: Chang Gung Memorial Hospital completed the first human pancreas transplant in Asia.