Between 1914 and 1918 the whole of Europe was plunged into an event that would forever shape the future of the planet: the First World War. Europe was divided into two blocks. The Triple Alliance, a purely defensive agreement between Austria-Hungary, Germany and Italy signed in 1882 and the Triple Entente, consisting of Britain, France and Russia. The Entente was created with the intention to form a common front against the Austro-German expansion into Morocco and the Balkans.
On June 28th, 1914, Archduke Franz Ferdinand of Austria and his wife were killed in Sarajevo. The assassin was Gavrilo Princip, a student nationalist and part of the "Mlada Bosna" organization which was in favor of the annexation of Bosnia to Serbia. Using the attack as a pretext, Austria, attacked Serbia on June 28th, 1914. Russia, sworn to defend Serbian independence, is forced to intervene. A few days later on August 3rd, Germany declared war on France. Now the two had joined the Central Powers in a war against the forces of the Triple Entente. Germany attempted to attack France through the weakened borders of Belgium, a neutral country. This maneuver prompts Britain to enter into the conflict, as it refuses to tolerate an assault on a neutral country on the coast overlooking the English Channel. At the same time, Russia attacked East Prussia, bringing aabout a series of humiliating Russian defeats. Although initially neutral, Italy decided to side with the forces of the Entente to free Trentino, Istria and Dalmatia, still in Austrian hands. On May 23rd 1915, Italy entered into war with Austria. After an initial phase of great movement, the warring fronts became immobilized and a long and exhausting war began in the trenches. As a result of the Bolshevik Revolution, Russia opted out of the war in December of 1917. The Germans repositioned troops from the Russian front to the Western Front.
Between the end of 1917 and the first months of 1918, the Central Powers launched a series of offensives. But they had problems within their own countries: the people of the Habsburg Empire were on the verge of a revolt, and Germany was on the verge of economic collapse. It was the beginning of the end. The offensive maneuvers from the central block slowly became less effective while the strength of the Triple Entente was bolstered by soldiers arriving from the United States, fighting hard along all fronts.
Between October and November of 1918, the Central Powers were forced to surrender. The Great War had cost nearly twenty million lives. The dissolution of the Austro-Hungarian Empire, in deference to the principle of nationality, saw the creation of many new states in Austria and Hungary. Czechoslovakia was formed from Bohemia, Moravia and Slovakia. Transylvania becomes part of Romania. South Tyrol and Trieste became Italian. Galicia was transferred to Poland, while Slovenia, Herzegovina, Croatia and Vojvodina joined Bosnia, Montenegro and Macedonia formed the Kingdom of Serbs, Croats and Slovenes. The Treaty of Versailles imposed upon Germany included heavy and costly war reparations. The statutes of the treaty humiliate the country and would sew the seeds of for revenge.