World War I was the result of several decades of increasing tensions in Europe due to rising nationalism, imperial pursuits, and arms proliferation. These factors, coupled with a rigid alliance system, required only a spark to place the continent on the road to war. This spark came on July 28, 1914, when Gavrilo Princip, a member of the Serbian Black Hand, assassinated Archduke Franz Ferdinand of Austria-Hungary in Sarajevo. In response, Austria-Hungary issued the July Ultimatum to Serbia which made demands that no sovereign nation could accept. The Serbian refusal activated the alliance system which saw Russia mobilize to aid Serbia. This led to Germany mobilizing to aid Austria-Hungary and then France to support Russia.
With the outbreak of hostilities, Germany sought to utilize the Schlieffen Plan which called for a quick victory against France so that troops could be moved east to fight Russia. The first step of this plan called for German troops to move through Belgium. This action led to Britain entering the conflict as it was obligated by treaty to defend the small nation. In the resulting fighting, the Germans nearly reached Paris, but were halted at the Battle of the Marne. In the east, Germany won a stunning victory over the Russians at Tannenberg, while the Serbs threw back an Austrian invasion of their country. Though beaten by the Germans, the Russians won a key victory over the Austrians as the Battle of Galicia.
With the beginning of trench warfare on the Western Front, Britain and France sought to break through the German lines. Wishing to focus its attention on Russia, Germany launched only limited attacks in the west where they debuted the use of poison gas. In an effort to break the stalemate, Britain and France conducted major offensive operations at Neuve Chapelle, Artois, Champagne, and Loos. In each case, no breakthrough occurred and casualties were heavy. Their cause was bolsterd in May when Italy entered the war on their side. In the east, German forces began operating in concert with the Austrians. Unleashing the Gorlice-Tarnow Offensive in May, they inflicted a severe defeat on the Russians and forced them into a full retreat.
A big year on the Western Front, 1916 saw two of the bloodiest battles of the war as well as the Battle of Jutland, the only major clash between the British and German fleets. Not believing that a breakthrough was possible, Germany began a battle of attrition in February by assaulting the fortress city of Verdun. With the French under heavy pressure, the British launched a major offensive at the Somme in July. While the German attack at Verdun ultimately failed, the British suffered horrific casualties at the Somme for little ground gained. While both sides were bleeding in the west, Russia was able to recover and launched the successful Brusilov Offensive in June.
While the armies clashed in Europe, fighting also raged across the belligerents' colonial empires. In Africa, British, French, and Belgian forces captured the German colonies of Togoland, Kamerun, and South-West Africa. Only in German East Africa was a successful defense mounted, where Colonel Paul von Lettow-Vorbeck's men held out for the duration of the conflict. In the Middle East, British forces clashed with the Ottoman Empire. After the failed campaign at Gallipoli, the primary British efforts came through Egypt and Mesopotamia. After victories at Romani and Gaza, British troops pushed into Palestine and won the key Battle of Megiddo. Other campaigns in the region included fighting in the Caucasus and the Arab Revolt.
Their offensive capability spent at Verdun, the Germans opened 1917 by falling back to a strong position known as the Hindenburg Line. The Allied cause was bolstered in April when the United States, angered by Germany's resumption of unrestricted submarine warfare, entered the war. Returning to the offensive, the French were badly repulsed later that month at Chemin des Dames leading some units to mutiny. Forced to carry the load, the British won limited victories at Arras and Messines, but suffered heavily at Passchendaele. Despite some success in 1916, Russia began to collapse internally as revolution broke out and the Communist Bolsheviks came to power. Seeking to exit the war, they signed the Treaty of Brest-Litovsk in early 1918.
With troops from the Eastern Front freed for service in the west, German General Erich Ludendorff sought to inflict a decisive blow on the tired British and French before American troops could arrive in large numbers. Launching a series of Spring Offensives, the Germans stretched the Allies to brink but were unable to break through. Recovering from the German onslaughts, the Allies counterattacked in August with the Hundred Days Offensive. Slamming into the German lines, the Allies won key victories at Amiens, Meuse-Argonne, and shattered the Hindenburg Line. Forcing the Germans into full retreat, Allied forces compelled them to seek an armistice on November 11, 1918.
Opening in January 1919, the Paris Peace Conference was convened to draft the treaties that would officially end the war. Dominated by David Lloyd George (Britain), Woodrow Wilson (US), and Georges Clemenceau (France), the conference re-drew the map of Europe and began to design the postwar world. Having signed the armistice under the belief that they would be able to negotiate a peace, Germany was angered when the Allies dictated the terms of the treaty. Despite the wishes of Wilson, a harsh peace was inflicted on Germany which included a loss of territory, military restrictions, heavy war reparations, and acceptance of sole responsibility for the war. Several of these clauses helped create the circumstance that led to World War II.
The battles of the World War I were fought across the globe from the fields of Flanders and France to the Russian plains and deserts of the Middle East. Beginning in 1914, these battles devastated the landscape and elevated to prominence places that had previously been unknown. As a result, names such as Gallipoli, the Somme, Verdun, and Meuse-Argonne became eternally entwined with images of sacrifice, bloodshed, and heroism. Due to the static nature of World War I trench warfare, fighting took place on a routine basis and soldiers were rarely safe from the threat of death. During World War I, over 9 million men were killed and 21 million wounded in battle as each side fought for their chosen cause.