During WWI, the Spanish flu caused about 1/3 of total military deaths.

U-boat is the anglicized (and shortened) version of the German word "Unterseeboot", meaning literally "undersea boat".

The Choctaw code talkers were a group of Choctaw Indians from Oklahoma who pioneered the use of Native American languages as military code.

Little Willie was a prototype in the development of the British Mark I tank. Built in 1915, it carried a crew of three and could travel as fast as 3 mph.

Woodrow Wilson's campaign slogan was "He kept us out of war" when he ran for re-election in 1916 against Charles Evans Hughes. Five months after his re-election, he asked congress to declare war on the Central Powers.

Shell shock is a term coined to describe the reaction of some soldiers in World War I to the trauma of battle. While some soldiers recovered, others suffered for the rest of their lives.

RMS Lusitania was a British ocean liner that was sunk by a German submarine. The sinking helped shift public opinion in the United States against Germany, and was a factor in the United States' declaration of war nearly two years later.

WWI was fought from 1914-1918 on every ocean and on almost every continent. Most of the fighting, however, took place in Europe.

The "Harlem Hellfighters" were the first all-black regiment in WWI. They earned their nickname from the Germans due to their toughness and the fact that they never lost a man through capture, lost a trench or a foot of ground to the enemy.

On March 3, 1918, the Bolshevik party which had come into power largely by playing on national discontent with the war, agreed to the Treaty of Brest-Litovsk, effectively pulling Russia out of World War I. The terms of the treaty were harsh, however, and Russia gave up vast territories to Germany including Finland, Poland, and the Ukraine.