World War I Fast Facts

CNN Editorial Research

Updated 1312 GMT (2112 HKT) July 20, 2021

World War I ushered in an era of chemical weapons use that lingers, lethally, into the present day. About 1 million casualties were inflicted, and 90,000 were killed. Here, French troops wear an early form of gas mask in the trenches during the first widespread use of gas, by the Germans at the Second Battle of Ypres in 1916.

Photos: Photos: WWI chemical weapons

Chemical weapons in World War I – World War I ushered in an era of chemical weapons use that lingers, lethally, into the present day. About 1 million casualties were inflicted, and 90,000 were killed. Here, French troops wear an early form of gas mask in the trenches during the first widespread use of gas, by the Germans at the Second Battle of Ypres in 1916.

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French soldiers making a gas and flame attack on German trenches in Flanders, Belgium, in 1918. German forces were the first to open valves on gas cylinders, releasing the toxic cloud on unprepared French troops in Ypres in 1915.

Photos: Photos: WWI chemical weapons

Chemical weapons in World War I – French soldiers making a gas and flame attack on German trenches in Flanders, Belgium, in 1918. German forces were the first to open valves on gas cylinders, releasing the toxic cloud on unprepared French troops in Ypres in 1915.

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The bodies of hundreds of Italian soldiers are strewn across the battlefield, victims of a gas and flame attack during World War I, as others haul the wounded on stretchers. They were members of the Ninth Italian Regiment of the Queen's Brigade.

Photos: Photos: WWI chemical weapons

Chemical weapons in World War I – The bodies of hundreds of Italian soldiers are strewn across the battlefield, victims of a gas and flame attack during World War I, as others haul the wounded on stretchers. They were members of the Ninth Italian Regiment of the Queen's Brigade.

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Early gas masks were often ineffectual. The Germans and Americans would ultimately be the most successful in creating barriers to lethal gases. A German soldier shows how to wear one version.

Photos: Photos: WWI chemical weapons

Chemical weapons in World War I – Early gas masks were often ineffectual. The Germans and Americans would ultimately be the most successful in creating barriers to lethal gases. A German soldier shows how to wear one version.

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A soldier demonstrates an ungainly French gas mask. "French masks were notoriously unreliable,"<a href="http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2376985/" target="_blank"> wrote</a> historian Gerald Fitzgerald.

Photos: Photos: WWI chemical weapons

Chemical weapons in World War I – A soldier demonstrates an ungainly French gas mask. "French masks were notoriously unreliable," wrote historian Gerald Fitzgerald.

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A German cavalry unit with both horses and soldiers wearing gas masks advances during the Second Battle of the Aisne at Soissons, France, in June 1918.

Photos: Photos: WWI chemical weapons

Chemical weapons in World War I – A German cavalry unit with both horses and soldiers wearing gas masks advances during the Second Battle of the Aisne at Soissons, France, in June 1918.

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A German soldier wears a more rudimentary gas mask in 1915. Although the Germans were first to deploy chemical weapons in the war, both sides were soon routinely using chlorine and other gases in battle.

Photos: Photos: WWI chemical weapons

Chemical weapons in World War I – A German soldier wears a more rudimentary gas mask in 1915. Although the Germans were first to deploy chemical weapons in the war, both sides were soon routinely using chlorine and other gases in battle.

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Men of the British Army's 55th Division, blinded by a poison gas attack, in April 1918. British soldier Wilfred Owen captured the panic of an attack in verse "Gas! Gas! Quick, boys! -- An ecstasy of fumbling, Fitting the clumsy helmets just in time; But someone still was yelling out and stumbling, And flound'ring like a man on fire or lime."

Photos: Photos: WWI chemical weapons

Chemical weapons in World War I – Men of the British Army's 55th Division, blinded by a poison gas attack, in April 1918. British soldier Wilfred Owen captured the panic of an attack in verse "Gas! Gas! Quick, boys! -- An ecstasy of fumbling, Fitting the clumsy helmets just in time; But someone still was yelling out and stumbling, And flound'ring like a man on fire or lime."

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(CNN)Here's some background information about World War I, also known as the First World War and the Great War, which lasted from 1914 to 1918.

Causes of World War I

The assassination of Archduke Franz Ferdinand of Austria-Hungary by Gavrilo Princip, a Bosnian Serb, led to Austria-Hungary declaring war on Serbia.

The Central Powers consisted of Austria-Hungary, Bulgaria, Germany and the Ottoman Empire (now Turkey).

The Allied Powers consisted of Belgium, France, Great Britain, Greece, Italy, Montenegro, Portugal, Romania, Russia, Serbia and the United States.

The United States declared neutrality until German submarine warfare threatened American commercial shipping.

US Troop Statistics

(Source: Defense Casualty Analysis System)
Battle deaths: 53,402
Non-battle deaths: 63,114
Total deaths: 116,516
Total US soldiers wounded: 204,002
Total number of US troops that served in the conflict: 4,734,991

Other Military Casualties by Country

(Source: Encyclopedia Britannica)
Austria-Hungary: 1,200,000 dead; 3,620,000 wounded
Belgium: 13,716 dead; 44,686 wounded
Bulgaria: 87,500 dead; 152,390 wounded
France: 1,357,800 dead; 4,266,000 wounded
Germany: 1,773,700 dead; 4,216,058 wounded
Great Britain: 908,371 dead; 2,090,212 wounded
Greece: 5,000 dead; 21,000 wounded
Italy: 650,000 dead; 947,000 wounded