The Events of WWI:
(Click the images to read the articles)

Unrestricted Submarine Warfare

The Zimmerman Note

http://www.history.com/this-day-in-history/germany-resumes-unrestricted-submarine-warfare

http://www.history.com/news/ask-history/what-was-the-zimmermann-telegram

The Battle of Verdun

Treaty of Brest-Litovsk

http://www.bbc.co.uk/history/worldwars/wwone/battle_verdun.shtml

http://www.historylearningsite.co.uk/treaty_of_brest-litovsk.htm

Second Battle of the Marne

http://www.history.com/this-day-in-history/second-battle-of-the-marne-begins-with-final-german-offensive