Special Report

The World War I Participants With the Smallest and Biggest Armies

Samuel Stebbins

Published: November 24, 2023 11:42 am

The convergence of new military technologies and antiquated combat strategies in the First World War brought a level of death and destruction never before seen in human history. From July 1914 through November 1918, the conflict resulted in the toppling of three monarchies, the dissolution of four empires, and nearly 20 million military and civilian deaths.

Waged with heavy artillery, machine guns, tanks, and chemical weapons, the fighting was largely confined to continental Europe – but drew in military powers from other parts of the world, including Asia and North America. (These 12 military strategies changed the course of history.)

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. 

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. 

Among the countries and empires on this list, total troop mobilization ranged from 50,000 to about 12 million. Casualty counts by military power also varied considerably, with Germany and Russia each reporting over 1.5 million troop fatalities, the most of any country in the war. 

The result of diplomatic failures, miscalculations, and distrust among European powers, World War I 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 been the war to end all wars. (These 29 countries are at war right now.)

Here are the biggest armies of WWI.

16. Montenegro

Source: Paul Thompson/FPG / Archive Photos via Getty Images

• 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)

15. Portugal

Source: FPG / Getty Images

• 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)

14. Greece

Source: Topical Press Agency / Archive Photos via Getty Images

• 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

Belgian troops at the barricad... (CC BY 2.0) by Thomas Quine

• 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)

12. Bulgaria

Source: Paul Thompson/FPG / Archive Photos via Getty Images

• 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)

11. Serbia

Source: Paul Thompson/FPG / Archive Photos via Getty Images

• 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)

10. Romania

Source: Hulton Archive / Hulton Archive via Getty Images

• 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)

9. Japan

Source: A. R. Coster / Hulton Archive via Getty Images

• 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)

8. Ottoman Empire (Turkey)

Source: FPG / Archive Photos via Getty Images

• 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)

7. United States

Source: Paul Thompson/FPG / Archive Photos via Getty Images

• 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)

6. Italy

Source: FPG / Archive Photos via Getty Images

• 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)

5. Austria-Hungary

Source: Paul Thompson/FPG / Getty Images

• 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)

4. British Empire

Source: Topical Press Agency / Getty Images

• 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)

3. France

Source: Paul Thompson/FPG / Getty Images

• 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)

2. Germany

Source: Keystone / Hulton Archive via Getty Images

• 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)

1. Russia

Source: FPG / Archive Photos via Getty Images

• 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)