The war began after the assassination of Archduke Franz Ferdinand of Austria. That triggered a bunch of alliances, and countries quickly got pulled into the conflict. Most of the fighting took place in Europe, with brutal trench warfare on the Western Front. Millions of soldiers died, and entire cities were destroyed.

New technology like tanks, airplanes, and poison gas made the war even deadlier. In 1917, the U.S. entered the war on the side of the Allies, and that helped tip the balance. The war ended in 1918 when Germany signed an armistice, leading to the Treaty of Versailles in 1919, which placed heavy blame and reparations on Germany.

The war had a huge impact on the world, leading to the downfall of empires, the rise of new nations, and setting the stage for World War II.