August 26–30, 1914 · Eastern Front Theater

Two Russian armies invaded East Prussia at the war's outbreak, threatening to overwhelm German defenses. Generals Hindenburg and Ludendorff, summoned to command, exploited the Russian generals' failure to communicate securely — their radio messages were transmitted unencrypted. Using Germany's railway network to shift forces rapidly, they encircled General Samsonov's Second Army completely. 92,000 Russians were captured; Samsonov walked into the forest and shot himself. The First Army escaped but was crippled at the subsequent Battle of the Masurian Lakes.

September 5–12, 1914 · Western Front Theater

German forces had swept through Belgium and Luxembourg in six weeks, advancing within 30 miles of Paris. Then the French and British counterattacked along the Marne River, exploiting a gap between two German armies. The famous 'Taxis of the Marne' ferried French troops to the front. The German advance halted, and both sides dug in. The war of movement was over.

October 19 – November 22, 1914 · Western Front Theater

Germany's last attempt in 1914 to break through Allied lines before winter. Young German volunteers — students and recent graduates — charged British professional soldiers at Langemarck in what Germans later called the Kindermord (Massacre of the Innocents). The Allies held, but the prewar British Expeditionary Force was nearly annihilated.

April 25, 1915 – January 9, 1916 · Middle East Theater

Winston Churchill's bold plan to knock the Ottoman Empire out of the war by seizing the Dardanelles Strait and capturing Constantinople. ANZAC (Australian and New Zealand) and British troops landed on the Gallipoli Peninsula but were pinned on the beaches by Turkish defenders under Mustafa Kemal. Eight months of futile fighting in the hills followed before evacuation.

February 21 – December 18, 1916 · Western Front Theater▶ Animated map

Germany's plan was not to capture Verdun but to 'bleed France white' — to force the French to feed so many men into the battle that the French army would collapse. The battle lasted 303 days, the longest of the war. France held, but at catastrophic cost. The landscape was so devastated by shells that it remains uninhabitable today.

May 31 – June 1, 1916 · North Sea Theater

The only major fleet engagement of the war, fought off the coast of Denmark. Germany's High Seas Fleet inflicted greater losses on the Royal Navy but failed to break the British blockade. The German fleet retreated to port and never challenged Britain's naval supremacy again. Winston Churchill said Jellicoe was the only man who could lose the war in an afternoon.

June 4 – September 20, 1916 · Eastern Front Theater

The most successful Allied offensive of WWI. Russian General Brusilov attacked on a wide front using coordinated infantry and artillery, bypassing strongpoints rather than battering them. Austria-Hungary suffered catastrophic losses — over 600,000 captured — and never fully recovered as a fighting force. The offensive helped bring Romania into the war and relieved pressure on Verdun.

July 1 – November 18, 1916 · Western Front Theater▶ Animated map

Launched to relieve pressure on Verdun, the Somme became the war's most notorious battle. On July 1st — the bloodiest day in British military history — 57,470 British soldiers were killed or wounded in a single day. A week-long artillery bombardment had failed to destroy the deep German bunkers; men walked into uncut barbed wire and undamaged machine guns. The battle lasted four months for a maximum advance of seven miles.

July 31 – November 10, 1917 · Western Front Theater

Haig's attempt to break through the German lines in Flanders and reach the Belgian coast. Preliminary bombardment destroyed the drainage system, turning the battlefield into a liquid mud swamp. Men and horses drowned in shell craters. The Canadians finally captured the ruined village of Passchendaele after three months, gaining five miles at a cost of 325,000 British casualties.

October 24 – November 19, 1917 · Italian Front Theater

A combined German-Austrian assault using new 'stormtrooper' infiltration tactics broke the Italian line completely. The Italian army collapsed, retreating 100 miles in two weeks. 275,000 Italian soldiers were captured. Ernest Hemingway, who served as an ambulance driver on the Italian front, later fictionalized the retreat in A Farewell to Arms.

November 20 – December 7, 1917 · Western Front Theater

The first large-scale use of tanks in warfare. On November 20, 476 British tanks advanced without a preliminary artillery bombardment, achieving complete surprise and breaking through the Hindenburg Line — church bells were rung in London for the first time since 1914. But the exploitation failed for lack of fresh troops; the cavalry could not advance through the broken ground. On November 30, Germany counterattacked with stormtrooper infiltration tactics, regaining most of the lost ground within days.

March 21 – April 5, 1918 · Western Front Theater

With Russia knocked out of the war, Germany transferred 50 divisions west for a last desperate gamble before American troops arrived in strength. Using stormtrooper infiltration tactics, they smashed through British lines, advancing up to 40 miles — more ground than anyone had taken in three years. Paris was shelled by a 75-mile-range gun. Then momentum stalled as supply lines couldn't keep up.

July 15 – August 6, 1918 · Western Front Theater

Germany's last offensive of the war — Ludendorff's 'Peace Offensive.' French intelligence obtained the exact date and time of attack. General Gouraud deliberately thinned his front line, pulling his main force back — the German barrage and assault fell largely on empty trenches. When German forces crossed the Marne, a massive French-American counterattack, Operation Marneschutz-Reims, smashed the assault. Marshal Foch then launched a devastating counteroffensive that pushed Germany back 40 miles in three weeks.

September 19–25, 1918 · Middle East Theater

British and Empire forces under Allenby shattered the Ottoman army in Palestine. Using cavalry, aircraft, and coordinated infantry in a masterful combined-arms operation, Allenby destroyed three Ottoman armies in a week. Damascus fell on October 1st. T.E. Lawrence and the Arab Revolt rode alongside, entering cities in triumph.

August 8 – November 11, 1918 · Western Front Theater

The war-ending Allied offensive began on August 8 — 'the Black Day of the German Army,' as Ludendorff called it. Using tanks, aircraft, artillery, and infantry in coordinated combined-arms attacks, the Allies broke through German lines repeatedly. Germany's army disintegrated; soldiers surrendered by the hundreds of thousands. On November 11 at 11am, the guns fell silent.