Causes of WW1

Causes:
a) Militarism: militarism is the belief that a country should be militarily strong.  There is usually a strong tradition of military members in most families of the country.  The military is an honorable thing, and involvement is strongly encouraged for young adults.  It is also the belief that the country can and should use the military to protect itself and promote national interests.
b) Alliances: There were many alliances made throughout Europe that pulled almost every country into the war.  Serbia and Austria went into conflict, and all the alliances were put into effect.
c) Imperialism: This was also a motivator in the cause of the war because the victory pot included some very resource rich colonies.  Gaining control over these colonies would help the countries economy greatly and help in their international affairs.  Other countries would see that they have power and should be respected as a country.
d) Nationalism: Nationalism is the belief that a residents country is the best in the world.  This lead to all the European countries believing that they could not be defeated in a war.  The press also had a big hand in nationalism.  They began publishing  stuff that fueled nationalism.  Eventually this developed into the thoughts that their government was right, and that they could not be defeated in a war.  Europe was now a powder keg that was just waiting for one spark to set it off.

Spark of War: Austro-Hungarian Archduke Franz Ferdinand was assassinated by a Serbian terrorist by the name of Gavrilo Princip.  Th Serbians were mad that Austria-Hungary would not let the slavic provinces join with Serbia.  The terrorists then decided to assassinate the Archduke.  The Serbian military officers stood by the terrorists actions, prompting an ultimatum from the Austro-Hungarian government.  The Serbian government then rejected the ultimatum, causing Austria-Hungary to declare war on Serbia, starting the First World War.

Other:
a) Unrestricted Submarine Warfare (1915): Unrestricted Submarine Warfare was a military strategy instituted by the Germans during WW1.  The Germans promised to sink any armed ships in the Atlantic Ocean, but spare passenger ships.
b) Lusitania (sunk May 7, 1915): The RMS Lusitania was a passenger ship that was sunk by German U-Boats during the First World War.  This event prompted the USA to seriously consider entering the war on the side of the Entente.  A second explosion on the Lusitania would suggest that it was not only a passenger ship, but also a sneaky way for the Entente to carry weapons across the Atlantic.
c) Sussex Pledge (May 4th, 1916): The Sussex Pledge was made after  the French ship Sussex was sunk by German U-Boats.  This caused Germany to change its naval policies fearing that the US would enter the war.
d) Zimmermann Telegram (January 16, 1917): The Zimmermann Telegram was a note from German Foreign Secretary Arthur Zimmermann to Mexico.  The note was intended for Mexico, but was intercepted by British Intelligence.  The note asked that Mexico join the Central Powers in the case that the USA joined on the side of the Entente.  The note enraged the American public, and was a major cause in the USA joining the war in April.  Mexico never joined the war.