Prohibition of Alcohol (1920)
Prohibition was a nationwide constitutional ban on the production and sale of alcohol from 1920 until 1933. Pietistic protestants sought to heal society by directly combating alcoholism, political corruption, and family violence through the prohibition of alcohol. Needless to say, things did not go to plan. On December 5, 1933, prohibition was lifted with the ratification of the Twenty-first Amendment.
Spanish Flu (1918)
The 1918 Spanish flu pandemic lasted until 1920 and infected 500 million people—roughly a third of the world's population at the time—in four different waves. The death toll is estimated somewhere between 17 and 100 million, making it one of the deadliest pandemics in human history.