This year marks the centenary of the start of World War I. Thought of as the "war to end all wars," it left Europe in shambles, led to the deaths of over 9 million people, and drew in countries from every continent.

To commemorate the start of the war, Reuters has released previously unpublished photos of World War I that evoke the lives and struggles of ordinary soldiers during the world's first truly global war.

The pictures are the work of an unknown photographer, and were left behind on glass plates in various archives by a Viscount in the Armored Cavalry Branch of the French Army.

World War I was the most prominent example of trench warfare in history.

An undated archive picture shows French artillery officers on the phone relaying instructions to adjust cannon fire in a trench on the front line, at an unknown location in France. Denise Follveider/REUTERS

Trench warfare resulted from a revolution in firepower that was not matched by advances in mobility.

An undated archive picture shows French soldiers firing a 155 mm mortar from a trench on the front line, at an unknown location in France. Denise Follveider/REUTERS

Because of this discrepancy, the defensive position always had a clear advantage in battle.

An undated archive picture shows a French soldier aiming an anti-aircraft machine gun from a trench at Perthes les Hurlus, eastern France. Stringer ./REUTERS

The trenches, in which soldiers spent most of their time, were surrounded by razor wire to limit the effectiveness of an enemy trying to overrun the position.

An undated archive picture shows German soldiers (rear) offering to surrender to French troops, seen from a listening post in a trench at Massiges, northeastern France. Denise Follveider/REUTERS

Trenches could be hundreds of miles long, and would require constant upkeep.

An archive picture shows French officers inspecting trenches on the Argonne front, eastern France May 1916. Denise Follveider/REUTERS

They had special structures built for machine gunners.

An undated archive picture shows a shelter for machine gunners in a French trench at Apremont-la-Foret, eastern France. Denise Follveider/REUTERS

Here, French soldiers pose in a trench above Ablain-Saint-Nazaire on the Artois front in northern France.

An archive picture shows French troops in trenches above Ablain-Saint-Nazaire in the Artois front, northern France, in 1916. Denise Follveider/REUTERS

Outside of the trenches, soldiers built makeshift huts. This one was named "The Chalet."

An undated archive picture shows French soldiers posing outside their shack, called "The Chalet", at la Sapiniere near Lachalade on the Argonne front, eastern France. Denise Follveider/REUTERS

Because of the lack of progress in combat mobility, this French Cavalry Corps was made up of bicyclists.

An archive picture shows French cyclists of the Cavalry Corps, on the Champagne Front, Eastern France September 22, 1915. Denise Follveider/REUTERS

Limits on the availability of motorized engines led to the use of pack animals. Here, a dog pulls a Belgian machine gun.

An undated archive picture shows a dog pulling a Belgian machine gun at an unknown location in northern France. Denise Follveider/REUTERS

Since meals ready to eat (MREs) were not yet invented, soldiers had to prepare their own food on the front lines.

An undated archive picture shows carcasses of animals strung up before being cooked for soldiers, on the Champagne front, eastern France. Denise Follveider/REUTERS

Since trench warfare often resulted in a stalemate, soldiers did their best to adjust to their sometimes monotonous lives in the field. Here, a soldier leaves a shower at the rear guard house by the front lines. The sign reads "Thermal complex of the Poilu, showers, massages, chiropodist, manicurist. Free massages for women. "

An undated archive picture shows a French soldier after taking a shower, at the rear guard near the front line, at an unknown location in France. The placard reads "Thermal complex of the Poilu, showers, massages, chiropodist, manicurist. Free massages for women". Denise Follveider/REUTERS

To boost morale, shows were also performed ...

An archive picture taken shows soldiers attending an entertainment show at Suippes, on the Champagne Front, Eastern France in 1915. Denise Follveider/REUTERS

... as was Mass.