It was America's entrance into the conflict that ultimately turned it in the Allies' favor, and the US joined the victors in celebrating its end. Here, the famous "Lost Battalion" of the Argonne campaign marches down Fifth Avenue in New York City after returning home in spring 1919.
Source: National Geographic
The war ended on the 11th hour of the 11th day of the 11th month of the year in 1918, when the final armistice was signed. Here, people celebrate the war's end on the Grand Boulevard in Paris.
Merriment and camaraderie also endured. Here, German soldiers celebrate Christmas on the front line in 1914.
Amid the destruction and horror of World War I, some soldiers managed to maintain their humanity. Here, German soldiers carry wounded Canadian troops, who were fighting against them, to safety so they can recover in April 1917.
Caught between the advancing armies, civilians in Europe and elsewhere paid an enormous toll during the war. In this undated photo, Belgian refugees load onto boats in the port of Antwerp to escape the fighting in their country.
Even though the great powers were fighting largely in Europe, they exploited their colonial subjects around the world to supplement their own forces. Here, Indian soldiers are seen on banks of the Yser River in northern France with a traveling herd of goats they used to make their favorite dishes from home.
World War I also had far-reaching consequences outside of Europe, especially in the Middle East. This undated photo shows an officer of the Ottoman Empire, which entered the war on Germany and Austro-Hungary's side, conducting a military review in Damascus, Syria.
Source: BBC
Although World War I is often associated with the intense trench warfare on the Western Front, the war was waged in Eastern Europe as well. Here, soldiers rush into battle in Russia in 1917.
World War I was a total war — everything was a potential target, including Reims cathedral in France, pictured here amid falling bombs in September 1914.
The new industrial nature of the war laid waste to swathes of territory along the Western Front, illustrated by this nightmarish scene from the Battle of Argonne Forest on September 26, 1918, showing American soldiers in the east of France.
As the war progressed, previously unseen industrial weapons of war entered the conflict. This undated photo shows a German medic relieving victims of a gas attack.
For the first time in history, grueling trench warfare became a defining characteristic of war. A US artilleryman uses some downtime in a trench in France to write home to his family on March 7, 1918.
Battlefield engagements were stop-and-go in World War I. Here, a British soldier was stitching his shirt only be interrupted by a German shell landing nearby during the British army's advance toward Bapaume, France, sometime in 1918.
World War I officially began on July 28, 1914, after all the great powers of Europe formed two camps and issued declarations of war. Here, German soldiers leave Berlin for the Western Front on August 1, 1914, while women present them with flowers in gratitude.
This GIF shows how the war spread around the world.
Source: History Channel
