World War I (1914-1918)

Archduke Franz Ferdinand, heir to the Austro-Hungarian throne, and his wife Sophie were assassinated in Sarajevo by Gavrilo Princip, a Bosnian Serb nationalist. This event triggered the July Crisis that led to the outbreak of World War I.

After Serbia rejected key terms of a punitive ultimatum, Austria-Hungary declared war on Serbia. This activated the system of European alliances, drawing Russia, Germany, France, and Britain into the conflict within days.

Location: Vienna, Austria-Hungary

Germany declared war on Russia after Russia mobilized in support of Serbia. Germany then declared war on France (August 3) and invaded neutral Belgium to execute the Schlieffen Plan, bringing Britain into the war on August 4. Within a week, the major European powers were at war.

Location: Berlin, German Empire

French and British forces halted the German advance on Paris in the First Battle of the Marne, dashing German hopes for a quick victory. This battle established the stalemate on the Western Front, leading to four years of trench warfare.

Location: Marne River, France

The Ottoman Empire entered the war on the side of the Central Powers, opening fronts in the Caucasus, Mesopotamia, and the Dardanelles. This expanded the war beyond Europe and led to campaigns in Gallipoli, Palestine, and Arabia.

Location: Constantinople, Ottoman Empire

Germany launched the first large-scale chlorine gas attack at the Second Battle of Ypres, introducing chemical warfare to the battlefield. Over 5,000 Allied troops were killed by the gas in the initial assault. Both sides would use poison gas for the remainder of the war.

Location: Ypres, Belgium

Allied forces landed on the Gallipoli Peninsula in an attempt to capture Constantinople and open a supply route to Russia. The campaign turned into a months-long stalemate with heavy casualties on both sides, ending in an Allied evacuation in January 1916. The campaign became a defining moment for Australia and New Zealand (ANZAC).

Location: Gallipoli Peninsula, Ottoman Empire

A German U-boat torpedoed the British ocean liner RMS Lusitania off the coast of Ireland, killing 1,198 people including 128 Americans. The sinking turned international opinion against Germany and contributed to the eventual US entry into the war.

Location: Atlantic Ocean, near Ireland

Italy, which had been allied with Germany and Austria-Hungary before the war, declared war on Austria-Hungary and entered the conflict on the Allied side, opening the Italian front in the Alps.

Location: Rome, Italy

Germany launched a massive offensive against the French fortress of Verdun, intending to 'bleed France white.' The battle lasted 10 months, becoming the longest and one of the most costly battles of the war, with over 700,000 casualties. The French held the fortress.

Location: Verdun, France

The British Royal Navy's Grand Fleet and the German High Seas Fleet clashed off the coast of Denmark in the largest naval battle of the war. While Germany claimed a tactical victory (more ships sunk), the British maintained their naval blockade of Germany.

Location: North Sea, near Jutland

The British and French launched a major offensive on the Somme River. On the first day alone, the British suffered 57,470 casualties - the bloodiest day in British military history. The battle continued until November, with over one million casualties and minimal territorial gains.

Location: Somme River, France

German Foreign Secretary Arthur Zimmermann sent a secret telegram to Mexico proposing a military alliance against the United States, promising Mexico the return of Texas, New Mexico, and Arizona. The telegram was intercepted and decoded by British intelligence, inflaming American public opinion.

Location: Berlin, German Empire

Mass protests in Petrograd over food shortages and war fatigue escalated into a revolution. Tsar Nicholas II abdicated on March 15, ending the Romanov dynasty's 304-year rule. A provisional government took power, pledging to continue the war.

Location: Petrograd, Russian Empire

The United States declared war on Germany, citing unrestricted submarine warfare and the Zimmermann Telegram. The American entry provided the Allies with fresh troops, resources, and industrial capacity that would prove decisive in 1918.

Location: Washington, D.C., USA

Vladimir Lenin's Bolsheviks overthrew the provisional government in the October Revolution, promising 'peace, land, and bread.' The new Soviet government immediately sought to withdraw Russia from the war.

Location: Petrograd, Russia

US President Woodrow Wilson outlined his Fourteen Points for a post-war peace settlement, including open diplomacy, freedom of the seas, self-determination for nations, and the creation of a League of Nations. These principles shaped the post-war negotiations.

Location: Washington, D.C., USA

Soviet Russia signed the Treaty of Brest-Litovsk with the Central Powers, surrendering vast territories (including Ukraine, Finland, the Baltic states, and Poland) in exchange for peace. This freed German troops for a final offensive on the Western Front.

Location: Brest-Litovsk, Russia

The Allied forces launched the Meuse-Argonne Offensive, the final major Allied offensive of the war. Over one million American troops participated. The offensive, combined with Allied advances across the front, broke German resistance and triggered the collapse of the Central Powers.

Location: Argonne Forest, France

The Armistice was signed between the Allies and Germany at 5:00 AM, taking effect at 11:00 AM (the 'eleventh hour of the eleventh day of the eleventh month'). Hostilities ceased, ending four years of unprecedented bloodshed. The German Kaiser had abdicated two days earlier.

Location: Compiegne, France

The Treaty of Versailles was signed, officially ending the state of war with Germany. Germany accepted sole responsibility for the war (Article 231), lost territory, was forced to pay massive reparations, and had its military severely restricted. The treaty's punitive terms contributed to German resentment and the rise of Nazism.

Location: Versailles, France