WW 1 causes

1.
Nationalism- The support of one nation, being loyal to your country.

 Alliance System- The formal support to help countries in case of danger, or war.

 Imperialism- The building power of taking over another colonies. Countries were arguing over colonies, this caused war.

Militarism- Its the preparation for war. At the time, britain had the strongest navy and germany was trying to expand their own army. This established strong preparation for the war.

2.

The spark of WWI was the assassination of archduke Franz Ferdinand. Also, the rivalry between Europe and a group of alliances. Because Archduke Ferdinand was killed, it led to Austria-Hungary invading Serbia(where Franz Ferdinand was killed). Russia aided Serbia, and Germany declared war on Russia then. To help their allies, France started war on Austria-Hungary and Germany. England backed up their allies too, France and Russia. Then when the United States joined in, World War I officially began.

3.
-Unrestricted Sub Warfare: (1915-1918) A naval attack where submarines have the ability to sink ships without warning. There was no chance to get off the ship so all the crew sunk. Killed many ship members without having an actual cause. This is when US really wanted to join the war. 
-Lusitania: (May 7, 1915)  A ferry boat that transported merchandise and people from Great Britain and US. It after after being torpedoed by a German U-boat. This event really made the US want join the hectic war.

-Sussex Pledge: (May 4, 1916) A pledge Germany made, promising that they would sink any ships with their u-boats except if there was known weapons. unless there was weapons. The Lusitania was sunk three days after this pledge. This was another reason why the US should join the war.

-Zimmerman note: (1917) The note that was intercepted by the U.S. which was supposedly Germany trying to convince Mexico to attack the U.S.