When was World War I?

World War I spanned from the summer of 1914 to the autumn of 1918, though its causes stretched back decades and its consequences continued to unfold for generations. The precise dates frame a conflict that was unprecedented in scale, technology, and destructiveness.

The war began on June 28, 1914, with the assassination of Archduke Franz Ferdinand in Sarajevo, triggering a month of diplomatic crisis. Austria-Hungary declared war on Serbia on July 28. Russia mobilized on July 30. Germany declared war on Russia on August 1 and on France on August 3, invading Belgium on August 4, which brought Britain into the conflict. By the end of August 1914, the major European powers were locked in a war that most had expected to be over by Christmas.

The conflict evolved through distinct phases. The initial war of movement on the Western Front stalled by late 1914 into the trench warfare that would define the conflict. The year 1915 saw the expansion of the war — the disastrous Gallipoli campaign, Italy's entry on the Allied side, and the Armenian Genocide in the Ottoman Empire. In 1916, the battles of Verdun and the Somme produced over two million casualties combined for negligible territorial gain. The year 1917 was the war's turning point — the Russian Revolution, American entry, and the introduction of new tactics began shifting the balance. The final year, 1918, saw Germany's failed spring offensive followed by the Allied Hundred Days Offensive that broke German resistance.

The armistice of November 11, 1918, ended the fighting, but the formal peace came with the Treaty of Versailles on June 28, 1919 — exactly five years after the assassination that started it all. The war killed approximately 20 million people (roughly equally divided between military and civilian dead), wounded another 21 million, displaced millions more, destroyed four empires (German, Austro-Hungarian, Ottoman, and Russian), and created the conditions for an even more devastating conflict just two decades later.

The dates matter because they frame a before and after in human history. The world of 1918 was unrecognizable from the world of 1914 — not just politically, but psychologically. The optimism and confidence of pre-war European civilization was shattered, replaced by disillusionment, trauma, and the knowledge that industrial civilization could turn its productive power toward destruction on an unimaginable scale.