What was a major cause of world war i?

The major cause of World War I is "Imperialism".

Explanation:

Imperialism is the policy of establishing colonies away from the homeland and building an empire.Colonies provide raw material, market to sell manufactured goods and military strength for many European countries.France, Great Britain, Russia, America, and Germany all like to build a colonial empire.Imperialism led to frequent tussle among the great powers of Europe in all parts of the world.