page_title: World War I
section_title: Initial actions
hierarchical_section_title: World War I / Progress of the war / Eastern Front / Initial actions
context_page_description: World War I, also known as the First World War or the Great War, was a global war that lasted from 28 July 1914 to 11 November 1918. Contemporaneously described as "the war to end all wars", it led to the mobilisation of more than 70 million military personnel, including 60 million Europeans, making it one of the largest wars in history. It is also one of the deadliest conflicts in history, with an estimated nine million combatant deaths and 13 million civilian deaths as a direct result of the war, while resulting genocides and the related 1918 influenza pandemic caused another 17–100 million deaths worldwide.
  On 28 June 1914, Gavrilo Princip, a Bosnian Serb Yugoslav nationalist, assassinated the Austro-Hungarian heir Archduke Franz Ferdinand in Sarajevo, leading to the July Crisis. In response, Austria-Hungary issued an ultimatum to Serbia on 23 July. Serbia's reply failed to satisfy the Austrians, and the two moved to a war footing.
  A network of interlocking alliances enlarged the crisis from a bilateral issue in the Balkans to one involving most of Europe.
context_section_description: Russian plans for the start of the war called for simultaneous invasions of Austrian Galicia and East Prussia. Although Russia's initial advance into Galicia was largely successful, it was driven back from East Prussia by Hindenburg and Ludendorff at the battles of Tannenberg and the Masurian Lakes in August and September 1914. Russia's less developed industrial base and ineffective military leadership were instrumental in the events that unfolded. By the spring of 1915, the Russians had retreated from Galicia, and, in May, the Central Powers achieved a remarkable breakthrough on Poland's southern frontiers with their Gorlice–Tarnów Offensive. On 5 August, they captured Warsaw and forced the Russians to withdraw from Poland.
caption: Heir presumptive Karl visiting the fortress of Przemyśl after the first siege. The Russian Siege of Przemyśl was the longest siege of the war.
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