World War I was the result of leaders' aggression towards other countries, which was supported by the rising nationalism of the European nations. Economic and imperial competition, fear of war prompted military alliances and an arms race as well as the assassination of the archduke Francis Ferdinand, which further escalated the tension in the Balkans contributing to the outbreak of war.
World war 1 started on the 28th of June 1914 when Austria-Hungary declared war on Russia and ended on November 11th 1918. World war 1 was fought in Europe but did involve around 50 countries and 31 million men where over 7 million of them died with 2.6 million missing in action.
The menace of the hostile division led to an arms race, another cause of World War I. Acknowledging that Germany was the leader in military organization and efficiency, the great powers of Europe copied the universal conscription, large reserves and detailed planning of the Prussian system. Technological and organizational developments led to the formation of general staffs with precise plans for mobilization and attack that often could not be reversed once they were begun. …
