When Did World War 1 Start? Key Dates, Causes & Facts

A single bullet fired in Sarajevo on a summer morning in 1914 set off a chain reaction that would consume four years and drag in every major European power. Archduke Franz Ferdinand, heir presumptive to the Austro-Hungarian throne, was assassinated on 28 June 1914, sparking the diplomatic collapse historians call the July Crisis. Exactly one month later, Austria-Hungary declared war on Serbia, and the First World War had begun.

Start Date: 28 June 1914 · End Date: 11 November 1918 · Trigger Event: Assassination of Franz Ferdinand, 28 June 1914 · Initial Declaration: Austria-Hungary on Serbia, 28 June 1914 · Britain’s Entry: 4 June 1914

The key facts table below consolidates the pivotal dates and events that define the war’s timeline.

When and why did the World War 1 start?

World War 1 began on 28 July 1914 when Austria-Hungary declared war on Serbia, exactly one month after the assassination of Archduke Franz Ferdinand in Sarajevo (Defense Magazine). The assassination, carried out by Gavrilo Princip—a Bosnian Serb nationalist and member of the Black Hand—a Serbian nationalist group, provided the spark, but the war’s roots ran deeper than a single act of violence.

Assassination of Franz Ferdinand

At approximately 11:00 a.m. on 28 June 1914, Archduke Franz Ferdinand and his wife Sophie were shot while traveling through Sarajevo (Wikipedia – Assassination of Archduke Franz Ferdinand). The archduke died at 11:30 a.m., ten minutes after Sophie. Earlier that morning, a bomb attempt by Nedeljko Čabrinović—one of seven trained assassins—had failed, wounding 16–20 bystanders. Martial law was declared in Sarajevo the following day.

The assassination was the immediate catalyst, but alliances turned a regional dispute into a world war.

Austria-Hungary declares war on Serbia

On 23 July 1914, Austria-Hungary issued a harsh ultimatum to Serbia demanding sweeping concessions (Library of Congress). When Serbia accepted most demands but insisted on an independent investigation, Austria-Hungary declared war on 28 July 1914 and began mobilizing against its southern neighbor.

The July Crisis—the month of diplomatic maneuvering between the assassination and the declaration—saw Germany provide a “blank cheque” assurance to Austria-Hungary between 1–6 July 1914, emboldening Vienna to take a hard line (Wikipedia – July Crisis). Russia mobilized on 30 July 1914 to support Serbia, and the alliance system began its fatal cascade.

When did World War 1 start and end?

World War 1 lasted from 28 July 1914 to 11 November 1918—a span of 4 years, 3 months, and 14 days. The conflict evolved from a regional dispute between Austria-Hungary and Serbia into a global war between the Allied Powers and the Central Powers.

The European powers entered the war in rapid succession during the first week of August 1914. What began as an Austro-Serbian dispute became a continental conflict within days.

Key start declarations

Germany declared war on Russia on 1 August 1914, then on France on 3 August 1914, following the Schlieffen Plan’s invasion through Belgium (World History Encyclopedia). Britain declared war on Germany on 4 August 1914 after the German invasion of Belgium violated that nation’s neutrality (Imperial War Museums). Austria-Hungary declared war on Russia on 6 August 1914.

Armistice date

The fighting ended on 11 November 1918 when the Armistice was signed, halting combat on the Western Front. The formal peace treaty—the Treaty of Versailles—was signed in June 1919, officially ending the war with Germany.

When did World War 1 end?

The shooting stopped at 11:00 a.m. on 11 November 1918—the eleventh hour of the eleventh day of the eleventh month—when the Armistice between the Allies and Germany took effect. Four years of industrialized warfare had claimed an estimated 20 million lives.

Armistice signing

The armistice was signed in a railway carriage in the Forest of Compiègne, France, ending four years of brutal trench warfare. The agreement required Germany to withdraw its forces from occupied territories and surrender military equipment.

Treaty of Versailles

The formal peace settlement came in June 1919 with the Treaty of Versailles. Germany accepted responsibility for the war under Article 231—the “War Guilt Clause”—and agreed to pay reparations that would burden the Weimar Republic for decades.

Who won World War 1?

The Allied Powers—primarily Britain, France, the United States, Italy, and Japan—won World War 1. The Central Powers, led by Germany and Austria-Hungary, were defeated and dismantled.

Allied Powers victory

Britain’s Royal Navy dominated the seas throughout the war, enforcing a blockade that strangled German imports. American entry in April 1917 provided critical fresh troops and materiel, tipping the balance on the Western Front (Imperial War Museums). France and Britain bore the heaviest casualties during the attritional fighting, while Italy attacked Austria-Hungary from the south.

Central Powers defeat

Germany’s Spring Offensive of 1918 failed to break Allied lines before American forces arrived in force. Austria-Hungary collapsed into separate nation-states. The Ottoman Empire fell. Germany’s navy mutinied, triggering the Kaiser abdication and the establishment of the Weimar Republic.

When did World War 1 start in Europe?

The European powers entered the war in rapid succession during the first week of August 1914. What began as an Austro-Serbian dispute became a continental conflict within days.

Early declarations

Germany declared war on Russia on 1 August 1914, citing St. Petersburg’s mobilization. Three days later, Germany invaded neutral Belgium to execute the Schlieffen Plan, bringing Britain into the war. By 6 August 1914, Austria-Hungary had also declared war on Russia, completing the alliance trap.

Britain’s involvement

Britain entered the war on 4 August 1914, primarily to defend Belgian neutrality—a commitment dating to the 1839 Treaty of London. Britain’s declaration transformed a European war into a global conflict, drawing in colonies across Africa, Asia, and the Pacific (Imperial War Museums). Serbia doubled in size after the Balkan Wars of 1912–1913, making Austria-Hungary increasingly anxious about regional power shifts. For more information on the start of World War 1, check out this Adelaide Kane biography. Adelaide Kane biography

The alliance system—animated by Germany’s blank cheque and Russia’s support for Serbia—turned a regional dispute into a four-year global catastrophe.

The implications of the July Crisis extend well beyond the assassination itself. Seven assassins—trained in Serbia and coordinated through the Black Hand—participated in the plot, yet Austria-Hungary used the attack as a pretext to eliminate Serbian influence entirely. Serbia accepted most of the ultimatum’s demands, but Vienna was determined to act regardless.

Related reading: a.m.

While the spark ignited on 28 July 1914, World War 1’s causes, key battles and legacy reveal the complex alliances and strategies that prolonged the conflict across Europe.

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