Snippet from Wikipedia: World War I

World War I or the First World War (28 July 1914 – 11 November 1918), also known as the Great War, was a global conflict between two coalitions: the Allies (or Entente) and the Central Powers. Main areas of conflict included Europe and the Middle East, as well as parts of Africa and the Asia-Pacific. In Europe, the stalemate caused by trench warfare led to technological innovations such as tanks and aircraft, along with the widespread use of artillery, machine guns, and chemical weapons. One of the deadliest conflicts in history, it resulted in an estimated 30 million military casualties, plus another 8 million civilian deaths from war-related causes and genocide. The movement of large numbers of people was a major factor in the deadly Spanish flu pandemic.

The causes of World War I included the rise of Germany and decline of the Ottoman Empire, which disturbed the long-standing balance of power in Europe, and rising economic competition between nations driven by industrialisation and imperialism. Growing tensions between the great powers and in the Balkans reached a breaking point on 28 June 1914, when Gavrilo Princip, a Bosnian Serb, assassinated the heir to the Austro-Hungarian throne. Austria-Hungary blamed Serbia, and declared war on 28 July. After Russia mobilised in Serbia's defence, Germany declared war on Russia and France, who had an alliance. The United Kingdom entered after Germany invaded Belgium, and the Ottomans joined the Central Powers in November.

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Snippet from Wikipedia: First Battle of the Marne

The First Battle of the Marne or known in France as the Miracle on the Marne (French: miracle de la Marne) was a battle of the First World War fought from 5 to 12 September 1914. The German army invaded France with a plan for winning the war in 40 days by occupying Paris and destroying the French and British armies. The Germans had initial successes in August. They were victorious in the Battles of Mons and the Frontiers and overran a large area of northern France and Belgium. In what is called the Great Retreat the Germans pursued the retreating French and British forces more than 250 km (160 mi) southwards. The French and British halted their retreat in the Marne River valley, while the Germans advanced to 40 km (25 miles) from Paris.

With the battlefield reverses of August, Field Marshal John French, commander of the British Expeditionary Force (BEF), lost faith in the French and began to plan for a British retreat to port cities on the English Channel for an evacuation to Britain. Joseph Joffre, the French commander, maintained good order in his retreating army and was able to reinforce it with troops from his eastern flank and by integrating military reserve units into the regular army. By early September, the Franco–British forces outnumbered the Germans, who were exhausted after a month-long campaign, had outrun their supply lines and were suffering shortages. On 3 September, the military governor of Paris, Joseph Gallieni, perceived that the German right flank was vulnerable and positioned his forces to attack.

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