Archduke was a very high political person in Austria. He was assaniated along with his wife. This was one of the main reasons world war 1 started.

Entangling alliances is what I think was one of the main reasons, if not the top reason the war started. It starts with one country declaring war on another. Which brings there alliances in. So if Britian went to war with Germany, then Austria would go in on Germany's side and France and Belguim would be on Britians side.

This is when a country would go in an arms race and increase troops and weapons. They do this in case of war.

This means wanting to gain new land. Countries fought a lot in Africa and Asia for new land and raw materials. This tension would escalate and be on e of the major causes of the war.

Some people had to much pride in their country or nationalism, which isn't bad. But the countries try to outdue one another and reign dominance over the world which would build tension and increase the war coming. One issue of nationalism was the murder of Archduke Franz Ferdinand.

There was no world peace organization that could enforce peace. So war was the only way to settle disputes.