In which century was World War I?

In which century was World War I? The answer is the 20th century.

World War I was fought from July 28, 1914, to November 11, 1918, placing it firmly in the 20th century. It began after the assassination of Archduke Franz Ferdinand of Austria in Sarajevo, but deeper causes included rival alliances, imperial competition, militarism, and rising nationalism across Europe.

The conflict grew from a European crisis into a global war involving the Allied Powers and the Central Powers. Major fighting took place on the Western and Eastern Fronts, but campaigns also occurred in the Middle East, Africa, the Mediterranean, and the Asia-Pacific. Trench warfare, machine guns, heavy artillery, aircraft, tanks, and chemical weapons transformed modern combat.

The war ended with Germany’s armistice in 1918, although the postwar settlement continued through treaties negotiated in 1919 and afterward. The collapse of the German, Austro-Hungarian, Ottoman, and Russian empires reshaped international borders. A common mistake is to confuse the war’s 1914 start with the 19th century; the 20th century began in 1901, so every year of World War I belongs to it.