The main causes or reasons of World War first were Nationalism, imperialism, Alliances and militarism.
Explanation:
The First World War is commonly called as the Great War which prevailed in Europe from the year 1914 to 1918. The three continents- Europe, Asia and Africa participated and fought in this conflict. It is called World War because of the unprecedented number of countries were participating in it, its territory (in which it was fought) and the damage caused by it.
With the time of the end of the First World War, four major empires Russia, Germany, Austria-Hungary (Hapsburg) and Osmania were ruined. Due the heavy collapsed, the boundaries of Europe were recreated and the United States of America came up as a 'superpower' in the world.
