When World War I began in 1914, it brought a level of death and destruction never before seen in human history. New military technologies – including heavy artillery, machine guns, tanks, and chemical weapons – along with military strategies better suited to the previous century, turned much of Europe into the scene of horrific slaughter on an unprecedented scale.Â
By the time the war ended on Nov. 11, 1918, three monarchies were toppled, four empires were dissolved, and an estimated 9.7 million military personnel and another 10 million civilians were killed.
The result of poor diplomacy, political miscalculations, and distrust among European powers, the First World War, like many other violent conflicts, was entirely avoidable. Recognizing this, President Woodrow Wilson conceived of what would become the League of Nations, an international diplomatic group that would solve disputes before violence broke out. Had the League of Nations realized its vision, WWI may have truly been the war to end all wars. (Here is a look at 13 major wars happening around the world.)
Though fighting in the First World War was largely confined to continental Europe, the conflict eventually drew the involvement of military powers from other parts of the world, including Asia and North America.Â
Using data compiled by the Library of Congress, 24/7 Wall St. identified the countries with the largest armies in WWI. We ranked the 16 countries with available data on the total number of troops mobilized for the war effort. Casualty figures are also from the Library of Congress.Â
The belligerent powers of the war fought on one of two sides: the Allies, which included Russia, France, the British Empire, and the United States; and the Central Powers, which included Germany, Austria-Hungary, and the Ottoman Empire, now Turkey. Allied troop counts outnumbered that of the Central Powers by a wide margin, about 39.7 million to 19.5 million.Â
Among the countries and empires that were involved in the conflict, total troop mobilization ranged from 50,000 to about 12 million. Casualty counts by military power also varied considerably. Germany and Russia were the only countries to report more than 1.5 million troops killed. These two countries also had the largest armies during the war.Â
Total troop involvement does not always correlate with higher casualty figures, however. Though both the British Empire and France each mobilized approximately 7.5 million troops, the number of French personnel killed in battle was nearly 1.4 million, double the number of British troops killed. (Here is a look at the wars with the most U.S. military deaths.)
Click here to see the biggest armies of WWI.
Source: Paul Thompson/FPG / Archive Photos via Getty Images
16. Montenegro
> Troops mobilized: Approx. 50,000
> Troop contribution: 0.1% of Allied forces
> Troops killed: Approx. 3,000 (15th highest of 16 countries)
> Troops wounded: Approx. 10,000 (15th highest of 16 countries)
> Troops taken prisoner or missing: Approx. 7,000 (14th highest of 16 countries)
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Source: FPG / Getty Images
15. Portugal
> Troops mobilized: Approx. 100,000
> Troop contribution: 0.3% of Allied forces
> Troops killed: Approx. 4,000 (14th highest of 16 countries)
> Troops wounded: Approx. 15,000 (14th highest of 16 countries)
> Troops taken prisoner or missing: Approx. 200 (15th highest of 16 countries)
Source: Topical Press Agency / Archive Photos via Getty Images
14. Greece
> Troops mobilized: Approx. 230,000
> Troop contribution: 0.6% of Allied forces
> Troops killed: Approx. 15,000 (13th highest of 16 countries)
> Troops wounded: Approx. 40,000 (12th highest of 16 countries)
> Troops taken prisoner or missing: Approx. 45,000 (10th highest of 16 countries)
13. Belgium
> Troops mobilized: Approx. 267,000
> Troop contribution: 0.7% of Allied forces
> Troops killed: Approx. 20,000 (12th highest of 16 countries)
> Troops wounded: Approx. 60,000 (11th highest of 16 countries)
> Troops taken prisoner or missing: Approx. 10,000 (13th highest of 16 countries)
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Source: Paul Thompson/FPG / Archive Photos via Getty Images
12. Bulgaria
> Troops mobilized: Approx. 400,000
> Troop contribution: 2.1% of Central Powers forces
> Troops killed: Approx. 201,224 (9th highest of 16 countries)
> Troops wounded: Approx. 152,399 (9th highest of 16 countries)
> Troops taken prisoner or missing: Approx. 10,825 (12th highest of 16 countries)
Source: Paul Thompson/FPG / Archive Photos via Getty Images
11. Serbia
> Troops mobilized: Approx. 707,343
> Troop contribution: 1.8% of Allied forces
> Troops killed: Approx. 322,000 (7th highest of 16 countries)
> Troops wounded: Approx. 28,000 (13th highest of 16 countries)
> Troops taken prisoner or missing: Approx. 100,000 (8th highest of 16 countries)
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Source: Hulton Archive / Hulton Archive via Getty Images
10. Romania
> Troops mobilized: Approx. 750,000
> Troop contribution: 1.9% of Allied forces
> Troops killed: Approx. 200,000 (10th highest of 16 countries)
> Troops wounded: Approx. 120,000 (10th highest of 16 countries)
> Troops taken prisoner or missing: Approx. 80,000 (9th highest of 16 countries)
Source: A. R. Coster / Hulton Archive via Getty Images
9. Japan
> Troops mobilized: Approx. 800,000
> Troop contribution: 2.0% of Allied forces
> Troops killed: Approx. 300 (16th highest of 16 countries)
> Troops wounded: Approx. 907 (16th highest of 16 countries)
> Troops taken prisoner or missing: Approx. 03 (16th highest of 16 countries)
Source: FPG / Archive Photos via Getty Images
8. Ottoman Empire (Turkey)
> Troops mobilized: Approx. 1,600,000
> Troop contribution: 8.2% of Central Powers forces
> Troops killed: Approx. 300,000 (8th highest of 16 countries)
> Troops wounded: Approx. 570,000 (7th highest of 16 countries)
> Troops taken prisoner or missing: Approx. 130,000 (7th highest of 16 countries)
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Source: Paul Thompson/FPG / Archive Photos via Getty Images
7. United States
> Troops mobilized: Approx. 4,272,521
> Troop contribution: 10.8% of Allied forces
> Troops killed: Approx. 67,813 (11th highest of 16 countries)
> Troops wounded: Approx. 192,483 (8th highest of 16 countries)
> Troops taken prisoner or missing: Approx. 14,363 (11th highest of 16 countries)
Source: FPG / Archive Photos via Getty Images
6. Italy
> Troops mobilized: Approx. 5,500,000
> Troop contribution: 13.9% of Allied forces
> Troops killed: Approx. 460,000 (6th highest of 16 countries)
> Troops wounded: Approx. 947,000 (6th highest of 16 countries)
> Troops taken prisoner or missing: Approx. 1,393,000 (2nd highest of 16 countries)
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Source: Paul Thompson/FPG / Getty Images
5. Austria-Hungary
> Troops mobilized: Approx. 6,500,000
> Troop contribution: 33.3% of Central Powers forces
> Troops killed: Approx. 800,000 (4th highest of 16 countries)
> Troops wounded: Approx. 3,200,000 (3rd highest of 16 countries)
> Troops taken prisoner or missing: Approx. 1,211,000 (3rd highest of 16 countries)
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Source: Topical Press Agency / Getty Images
4. British Empire
> Troops mobilized: Approx. 7,500,000 (tied with France)
> Troop contribution: 18.9% of Allied forces
> Troops killed: Approx. 692,065 (5th highest of 16 countries)
> Troops wounded: Approx. 2,037,325 (5th highest of 16 countries)
> Troops taken prisoner or missing: Approx. 360,367 (6th highest of 16 countries)
Source: Paul Thompson/FPG / Getty Images
3. France
> Troops mobilized: Approx. 7,500,000 (tied with the British Empire)
> Troop contribution: 18.9% of Allied forces
> Troops killed: Approx. 1,385,300 (3rd highest of 16 countries)
> Troops wounded: Approx. 2,675,000 (4th highest of 16 countries)
> Troops taken prisoner or missing: Approx. 446,300 (5th highest of 16 countries)
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Source: Keystone / Hulton Archive via Getty Images
2. Germany
> Troops mobilized: Approx. 11,000,000
> Troop contribution: 56.4% of Central Powers forces
> Troops killed: Approx. 1,611,104 (2nd highest of 16 countries)
> Troops wounded: Approx. 3,683,143 (2nd highest of 16 countries)
> Troops taken prisoner or missing: Approx. 772,522 (4th highest of 16 countries)
Source: FPG / Archive Photos via Getty Images
1. Russia
> Troops mobilized: Approx. 12,000,000
> Troop contribution: 30.2% of Allied forces
> Troops killed: Approx. 1,700,000 (the highest of 16 countries)
> Troops wounded: Approx. 4,950,000 (the highest of 16 countries)
> Troops taken prisoner or missing: Approx. 2,500,000 (the highest of 16 countries)
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