The war that shattered the old order of Europe announced itself not with a grand declaration but with a single gunshot in a Bosnian street. On June 28, 1914, Gavrilo Princip, a Bosnian Serb nationalist, assassinated Archduke Franz Ferdinand, heir to the Austro-Hungarian throne, as his motorcade wound through Sarajevo. Within weeks, the carefully arranged alliances and obligations that European statesmen had spent decades constructing dragged one great power after another into a conflict that would kill between 15 and 22 million people before it was done.
The assassination was the spark, but the fuel had been accumulating for years. The rise of a newly unified and rapidly industrializing German Empire had disturbed the balance of power that had kept Europe relatively stable since the Napoleonic era. The slow decline of the Ottoman Empire left a power vacuum in southeastern Europe that Austria-Hungary and Russia both sought to fill, creating a series of crises in the Balkans that each time brought the continent closer to war. An arms race between the major powers intensified mutual suspicion, while competing imperial ambitions in Africa and Asia generated further friction. By the summer of 1914, the diplomatic architecture of Europe was so laden with mutual commitments that a conflict in one corner threatened to pull the entire structure down.
Austria-Hungary blamed Serbia for the assassination and issued an ultimatum so sweeping it was designed to be refused. When Serbia's reply failed to satisfy Vienna, Austria-Hungary declared war on July 28, 1914. Russia, which considered itself the protector of Slavic peoples, began to mobilize in Serbia's defense. Germany, bound by alliance to Austria-Hungary, declared war on Russia and then on France, which was linked to Russia by treaty. When German forces invaded neutral Belgium as part of the strategy to quickly knock France out of the war before turning to face Russia in the east, Britain entered the conflict in defense of Belgian neutrality. The Ottoman Empire joined the Central Powers in November, completing the opposing coalitions.
Germany's plan for rapid victory in the west collapsed at the Marne in September 1914. By the end of the year, both sides had dug into a nearly continuous line of trenches stretching from the English Channel to the Swiss frontier. This Western Front became the defining image of the war: a landscape of mud, barbed wire, and shattered trees where enormous offensives gained yards at the cost of hundreds of thousands of lives. The Eastern Front was more fluid, but neither the Central Powers nor the Allies could deliver a decisive blow despite repeated costly offensives.
The war introduced industrialized killing on a scale the world had never seen. Artillery grew to monstrous proportions, capable of flattening forests and obliterating entire villages in hours. Machine guns turned infantry assaults into slaughter. In April 1915, Germany used chlorine gas against Allied troops at Ypres, opening a terrible new chapter in warfare; both sides subsequently developed and deployed a variety of chemical agents, including mustard gas, against which no defense was fully effective. Tanks made their first appearance on the battlefield in 1916, lumbering across the moonscape of the Somme in an attempt to restore movement to a static war. Aircraft evolved from reconnaissance platforms into fighters, bombers, and ground-attack machines, adding a third dimension to a conflict that had previously been fought only on land and sea.
The battles of 1916 stand as the most devastating of the war. At Verdun, fought from February to December, French and German armies ground each other down in a struggle that cost nearly a million casualties combined. On the Somme, launched in July, the British and French forces suffered catastrophic losses on the first day alone — roughly 57,000 British casualties on July 1 — before the offensive ground to a halt with similarly enormous German losses. Yet neither battle broke the deadlock.
Italy, Bulgaria, Romania, and Greece entered the war at various points from 1915 onward, widening the theater of operations but not breaking the stalemate. The entry of the United States in April 1917, prompted by Germany's resumption of unrestricted submarine warfare against Atlantic shipping, eventually tipped the balance decisively. Fresh American troops began arriving in France in large numbers just as the Russian Empire collapsed from within. The Bolshevik revolution of October 1917 brought a new Soviet government to power that sought peace at any price; Russia signed an armistice in December and a separate peace at Brest-Litovsk in March 1918.
Freed from the Eastern Front, Germany launched a massive spring offensive in the west in March 1918. The attack drove deep into Allied lines but exhausted German forces without achieving a decisive breakthrough. The Allies responded with the Hundred Days Offensive beginning in August 1918, a relentless series of attacks that caused the German front to collapse. Bulgaria signed an armistice in late September. The Ottomans and Austria-Hungary followed in early November. With revolution threatening at home and the army spent, Kaiser Wilhelm II abdicated on November 9, and the guns fell silent on November 11, 1918.
The peace settlement that emerged from the Paris Peace Conference of 1919 to 1920 reshaped the map of the world. Germany lost significant territory, was required to disarm, and was burdened with heavy reparations under the Treaty of Versailles. The Russian, German, Austro-Hungarian, and Ottoman empires all dissolved, giving rise to new states including Poland, Finland, the Baltic nations, Czechoslovakia, and Yugoslavia. The League of Nations was established to prevent future wars, but its inability to manage the instabilities of the interwar period ultimately contributed to an even more destructive conflict just two decades later. Before that second catastrophe arrived, the events of 1914 to 1918 were simply known as the Great War, in the hope, now bitterly ironic, that no war could ever surpass it.
