Great War
1914-1918. Today called the First World War. The main war-waging parties were the Central Powers with Germany and Austria-Hungary on the one hand and the Triple Entente with Great Britain, France and Russia (and in 1917 the USA) on the other hand.
There were long- and short-term reasons for its outbreak. Long-term reasons were the naval race between Britain and Germany, the Moroccan Crisis and a strong belief in Social Darwinism among all nations. But the trigger for the outbreak of the war was the shooting of the Austrian heir to the throne, archduke Franz Ferdinand, and his wife by a Serbian nationalist in June 1914. This assassination caused Austria to declare war on Serbia. Germany as Austria's ally joined the war and so did Russia on Serbia's side. France and Britain followed. The different alliances were not forming automatically, but the days before the outbreak saw complex, frantic and often feavered negotiations between the powers.
While there was first enthusiasm on both sides, as all nations expected a short war, it soon turned out to be that they were fighting a war of attrition. The first 'modern' war as it was also called, brought about weapons of mass destruction, trench warfare, the use of poison gas and excessive, long battles, like the ones at Verdun or at the Somme.
All in all over six million soldiers died. The outcome of the war was decided, when the USA entered the war on the side of the Triple Entente in 1917. Germany finally asked for an armistice in November 1918 and was forced to accept the Treaty of Versailles in 1919. After the end of the Great War the face of Europe was to change forever, with the establishment of smaller nation states in Eastern Europe, the abolition of monarchy in Russia, Austria and Germany and more political power for women.
Britain still commemorates and honours the soldiers who died in the Great War on Remembrance Day or Armistice Day, November 11.
Sources:
Marwick, Arthur. War and Social Change in the Twentieth Century. London and Basingstoke: Macmillan, 1974.
Maurer, Michael. Kleine Geschichte Englands. Stuttgart: Reclam, 2007.