In 1918, the Spanish Influenza swept through the United States. The pandemic lasted from June 1918 to December 1920, spreading even to the Arctic and remote Pacific islands. Between 50 and 100 million died, making it one of the deadliest natural disasters in human history.
Aids
World War 2 diseases I am not familiar with, but the Spanish flu was an epidemic around the world at the end of World War 1.
Pneumonia
Not as good as it is now (2010) It was dirty and caused diseases
The cause was infectious diseases.
http://www.firstworldwar.com/ http://www.vlib.us/medical/ http://www.ralphmag.org/CG/world-war-one1.html
Gangrene, hepatitis, and trenches
the diseases caught by soldiers were nephritis, an inflammation of the kidney, and dysentery, the inflammation of the lining of the large intestines.
handwashing
It was most commonly known as "The Great War". It was the first time in history that more people died in war as a result of injuries than diseases.
The Spanish flu was the main disease during world war 1. Over 20 million people died from it. Between 50-100 million could have died from this disease.
Everyone pooped one monkeys and got diseases and died