Samuel Gompers, founder of the American Federation of Labor (AFL), discusses the effects of World War I on the United States.

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In a speech recorded from the battlefield in France on April 4, 1918, Gen. John J. "Black Jack" Pershing, commander of the American Expeditionary Forces during World War I, rallies American support with a patriotic message.

A look back at the legacy of World War I nearly 100 years after the conflict began.

In a Mail Call video, R. Lee Ermey answers a question from Mark of Kansas who wants to know what was in a World War I backpack. Ermey reveals that on top of all the other hardships WWI soldiers had to endure, their backpacks proved to be another annoyance. Men from the Great War Historical Society strapped on the WWI packs and completed some drills; by the end, they definitely felt the WWI soldiers pain. The bottom section of the backpack, known as the diaper, was detachable and carried the soldiers blanket, shelter half, and shelter half pole and pins. On the belt youd find ammo, a first aid kit, a canteen cover, and a canteen and cup. Inside the flaps were a baking tin, a condiment can, and boxes of bread rations. Also inside the flaps were a towel, soap dish, shaving kit, handkerchief, foot powder, and extra socks. Attached to the outside were the bayonet, shovel, trenching tool, and a mess kit. The entire weight of the pack lies entirely on the soldiers shoulders, making it very uncomfortable. If a soldier wanted to get anything out of his pack, he would have to stop, unravel everything, get what he needs, and then pack everything back up. Due to the placement of the bayonet, most soldiers would have to have a buddy put it back for them.

After running on the campaign, "He Kept Us Out of the War," Woodrow Wilson brings the United States into World War I in April 1917.

During World War I the governments of all the warring powers put enormous effort into scientific and technical development for military ends.

Very quickly, the power players in World War I understood they were fighting a world war, but perspectives on the conflict varied from country to country.