After sinking the RMS Lusitania, Germany realized they came dangerously close to bringing America into the war. Hoping to pacify the Americans, they agreed to the Sussex Pledge, where they promised to no longer attack civilian or neutral ships. Of course this agreement hampered the German war effort in the Atlantic, thus Germany quietly looked for a way to resume their unrestricted submarine warfare. The result was the infamous Zimmerman Telegram that did result in America joining the Allies.