World War I

The Assassination of Archduke Franz Ferdinand

Archduke Franz Ferdinand, heir to the throne of Austria-Hungary, and his wife Sophie were shot dead in Sarajevo by Gavrilo Princip, a 19-year-old Bosnian Serb nationalist. The killing came after an earlier bomb attempt failed and the couple's car took a wrong turn.

Why it matters: The assassination set off the chain of ultimatums and alliances known as the July Crisis, which within weeks plunged Europe into the First World War.

The July Crisis and the Outbreak of War

Backed by Germany, Austria-Hungary declared war on Serbia on 28 July. Europe's alliance system pulled in the great powers within days: Germany declared war on Russia on 1 August and on France on 3 August.

Why it matters: A regional Balkan quarrel became a continental war in barely a week, showing how the rival alliance blocs turned a single crisis into a general conflict.

Germany Invades Belgium

Following the Schlieffen Plan — Germany's strategy to knock out France quickly before turning east against Russia — German armies invaded neutral Belgium on 4 August to outflank the French defenses. The violation of Belgian neutrality brought Britain and its empire into the war that same day.

Why it matters: The invasion widened the war to include Britain and doomed Germany's hope of a short, decisive campaign in the west.

The Battle of Tannenberg

On the Eastern Front, a Russian invasion of German East Prussia ended in disaster at Tannenberg, where German forces under Hindenburg and Ludendorff encircled and destroyed the Russian Second Army, taking tens of thousands of prisoners.

Why it matters: Tannenberg was one of Germany's greatest victories of 1914 and made national heroes of Hindenburg and Ludendorff, who would come to dominate the German war effort.

The First Battle of the Marne

A French and British counterattack halted the German advance on Paris in the 'Miracle of the Marne.' The Germans fell back to the River Aisne and dug in; both sides then extended their trench lines to the sea.

Why it matters: The battle ended Germany's bid for a quick victory and began the trench-warfare stalemate that would define the Western Front for the next four years.

The Christmas Truce

Along parts of the Western Front, an unofficial and spontaneous truce broke out at Christmas 1914. British and German soldiers left their trenches to meet in no man's land, exchanging gifts, burying the dead, and in places playing impromptu football. It was not observed everywhere, and fighting continued in other sectors.

Why it matters: The truce became an enduring symbol of shared humanity amid the war; high commands on both sides later worked to prevent any such fraternization from happening again.

Poison Gas at the Second Battle of Ypres

At the Second Battle of Ypres, German forces released chlorine gas along a stretch of the Allied line — the first large-scale use of a lethal chemical weapon in the war. The gas broke the line held by French and Algerian troops, but Canadian units helped prevent a decisive breakthrough.

Why it matters: Ypres introduced poison gas as a weapon of mass terror to modern warfare; gas would be used by both sides for the rest of the war.

The Armenian Genocide

Beginning with the arrest of Armenian leaders in Constantinople on 24 April 1915, Ottoman authorities carried out the systematic destruction of the empire's Armenian population through massacres, death marches, starvation, and deportation. Of roughly 1.5 million Armenians in the empire, at least 664,000 and possibly up to 1.2 million were killed.

Why it matters: Often called the first genocide of the twentieth century, it was closely bound up with the events of the war in the Near East and remains a defining atrocity of the era.

How we know: Documented by the United States Holocaust Memorial Museum and other institutions; the estimated death toll spans a range.

The Gallipoli Campaign

Allied troops, including the Australian and New Zealand Army Corps (ANZAC), landed on the Gallipoli peninsula on 25 April 1915, aiming to force the Dardanelles and knock the Ottoman Empire out of the war. The campaign bogged down into months of costly stalemate and ended in an Allied evacuation by January 1916.

Why it matters: Gallipoli was a major Allied failure that cost hundreds of thousands of casualties, and it became a defining national memory for Australia and New Zealand, commemorated each year on ANZAC Day.

The Sinking of the Lusitania

The German submarine U-20 torpedoed the British ocean liner RMS Lusitania off the coast of Ireland without warning. The ship sank in under twenty minutes; of nearly 2,000 aboard, some 1,200 died, including 128 American citizens.

Why it matters: The deaths of American civilians caused international outrage and helped turn US public opinion against Germany — a step on the road to America's entry into the war.

The Battle of Verdun

The German chief of staff Erich von Falkenhayn launched a massive offensive against the French fortress city of Verdun, intending to 'bleed France white' in a battle of attrition. Over ten months the fighting killed or wounded hundreds of thousands on each side; the French held, and the German plan failed.

Why it matters: The longest battle of the war, Verdun became a symbol of French endurance and of the terrible, indecisive attrition of the Western Front.

The Battle of Jutland

The largest naval battle of the war pitted the British Grand Fleet against the German High Seas Fleet in the North Sea. In a confused, bloody action, Britain lost more ships and men, but the German fleet retreated and never again seriously challenged British control of the seas — so both sides claimed victory.

Why it matters: Jutland confirmed British naval dominance and preserved the blockade of Germany that steadily strangled its war economy.

The Battle of the Somme

The British-led offensive on the Somme opened on 1 July 1916 with the bloodiest day in the history of the British Army — around 57,000 casualties in a single day. The battle ground on for months for limited gains, and it saw the first-ever use of tanks in war in September 1916.

Why it matters: The Somme came to epitomize the industrial-scale slaughter of the Western Front and the human cost of trench warfare.

The Zimmermann Telegram

German Foreign Secretary Arthur Zimmermann sent a coded telegram proposing a military alliance with Mexico against the United States, offering to help Mexico regain territory in Texas, New Mexico, and Arizona. British codebreakers intercepted and decoded it and passed it to Washington; its publication in March 1917 inflamed American opinion.

Why it matters: Coming alongside Germany's renewed unrestricted submarine warfare, the telegram helped push the United States toward declaring war.

The United States Enters the War

Provoked by Germany's resumption of unrestricted submarine warfare and the Zimmermann Telegram, the United States declared war on Germany on 6 April 1917. President Woodrow Wilson framed American intervention as a way to shape a lasting peace.

Why it matters: American manpower, industry, and finance decisively tipped the balance toward the Allies over 1917–18.

The Battle of Passchendaele

The Third Battle of Ypres, known as Passchendaele, was a British offensive that aimed to break out of the Ypres salient. Heavy rain turned the battlefield into a sea of mud; over more than three months the Allies advanced about five miles at a cost of some 250,000 casualties.

Why it matters: Passchendaele became a byword for the futility and horror of the war, its muddy wasteland shaping enduring perceptions of the Western Front.

The Balfour Declaration

In a letter to Lord Rothschild, British Foreign Secretary Arthur Balfour declared that the government viewed 'with favour the establishment in Palestine of a national home for the Jewish people,' while pledging that nothing should prejudice the rights of the existing non-Jewish communities there.

Why it matters: Issued as Britain moved to take Palestine from the Ottomans, the declaration became a foundational and deeply contested document in the modern history of the Middle East.

The Russian Revolution

In 1917 Russia was convulsed by two revolutions: the February Revolution forced Tsar Nicholas II to abdicate, and in the October (November) Revolution the Bolsheviks under Lenin seized power. The new Soviet government sought to pull Russia out of the war.

Why it matters: The revolution removed Russia — the Allies' great eastern partner — from the war and created the world's first communist state, reshaping the twentieth century.

Wilson's Fourteen Points

In an address to Congress, President Woodrow Wilson set out Fourteen Points as a basis for a just and lasting peace — including open diplomacy, freedom of the seas, self-determination for peoples, and a general association of nations to guarantee security.

Why it matters: The Fourteen Points shaped the armistice negotiations and the postwar debate, and pointed toward the League of Nations — even as the eventual treaty fell far short of Wilson's vision.

The Treaty of Brest-Litovsk

Soviet Russia signed the Treaty of Brest-Litovsk with the Central Powers, formally withdrawing from the war. The terms were harsh: Russia surrendered vast western territories, including present-day Poland, the Baltic states, and Ukraine.

Why it matters: The treaty freed Germany to shift huge forces to the Western Front for a final gamble in 1918, while confirming Russia's exit from the war.

The German Spring Offensive

Reinforced by troops freed from the Eastern Front, General Ludendorff launched a series of massive offensives beginning on 21 March 1918, hoping to win the war before American forces arrived in strength. The Germans made dramatic gains but outran their supplies and could not deliver a knockout blow.

Why it matters: The failure of the Spring Offensive exhausted the German army and left it vulnerable to the Allied counterattacks that would end the war.

The Second Battle of the Marne

The last great German offensive of the war was halted near the Marne, and a powerful Allied counterattack — bolstered by fresh American troops — threw the Germans back. It marked the turning of the tide on the Western Front.

Why it matters: The Allied victory seized the initiative for good and led directly into the war-winning Hundred Days Offensive.

The Hundred Days Offensive

Beginning with the Battle of Amiens on 8 August 1918 — which Ludendorff called the 'black day of the German Army' — the Allies launched a series of coordinated offensives that broke through German defenses and drove the enemy into headlong retreat.

Why it matters: The Hundred Days shattered the German army's ability to fight on and forced Germany to seek an armistice.

The 1918 Influenza Pandemic

As the war ended, an exceptionally deadly influenza pandemic — the 'Spanish flu' — swept the world, spread in part by the movement of troops. It infected roughly a third of the global population and killed an estimated 50 million or more people, with about 675,000 deaths in the United States.

Why it matters: The pandemic killed more people than the war itself and struck the young and healthy with unusual severity, compounding the catastrophe of 1918.

The Armistice

Germany signed an armistice with the Allies in a railway carriage at Compiègne, France. The guns of the Western Front fell silent at 11 a.m. on 11 November 1918 — the eleventh hour of the eleventh day of the eleventh month.

Why it matters: The armistice ended the fighting of the First World War, which had killed some 9 million combatants; it is commemorated as Remembrance and Armistice Day.

The Treaty of Versailles

At the Paris Peace Conference, the victorious 'Big Four' — the United States, Britain, France, and Italy — dominated the drafting of the Treaty of Versailles. Germany was forced to accept strict terms: loss of territory and colonies, disarmament, reparations, and a 'war guilt' clause. The treaty also created the League of Nations. Germany signed on 28 June 1919, five years to the day after the Sarajevo assassination.

Why it matters: The harsh and contested peace reshaped the map of Europe and the Middle East, and its resentments would help set the stage for the Second World War.