World War I (also known as the First World War) was a global conflict set in Europe during 1918.
The United States suffered a deadly outbreak of Type A influenza, just as it was gearing up for the war. (Operation Hell Gate)
Mustard gas was used extensively in the conflict—primarily to terrorize enemy soldiers, who would retreat upon seeing its trademark yellow cloud. (Head Shot)
The aftermath of World War I saw the rise of communism, fascism, and Nazism. (Collateral Damage)