The root caused of World War 1 is because of  the  uneven development  of capital during imperialism period, resulting in the emerging imperialist countries urged to re-divide the world. In the late 19th and early 20th century,  from the stage of free competition of capitalism developed to a stage characterized by monopoly. Every country wants to maximum their profit,  actively promote the expansion and aggression of foreign policy, using force to fight for the colonial around the round.  Older colonial powers Britain, Russia, France and occupied most of the colonial world. Then the rapid economic development and expansion of national powers such as Germany,Japan, the United States and other emerging imperialist colonial countries have relatively little. This economic development and the uneven distribution of colonies led to sharp contradictions between the imperialist countries.