The four MAIN causes of war

Militarism where a nation believes in having a powerful army to have control over there people.

Alliances where nations join together during a time of war to fight against other nations who are a threat towards them. 

Imperialism where a large nation takes over smaller less powerful nations for a economical gain.

Nationalism where a country takes great pride in their nation and many people would go to war to expand their nation. 

In 1914 the Archduke Franz Fredinand who was the heir to the Austro-Hungarian throne was shot and kill why a terrorist group called the Black Hand. The assassination took place with a knowledge of Serbian officials who hoped to start war against the Austro-Hungarian empire.  If Austria attacked Serbia the Russians would help back them up.  So they had to get help from the Germans allies. 

This led to the start of ww1. 

1. Lusitania 1915 supply ship sent to Britain but was sunk by a German U-boat.

2.Sussex Pledge 1916 met the foreign policy goals of both Germany and Wilson by keeping the US out of the war longer.

3. Zimmermann note 1917 note sent from Germany to Mexico but was intercepted by Britain and sent to the US which made them get into the war. 

4. Unrestricted submarine warfare 1917 Germany continued trying to cut off the British by using their uboats.