Explanation: The primary events that led to the United States declaration of war against Germany were the Zimmerman Telegram and Germany's announced intention to resume unrestricted submarine warfare. American sentiment had leaned toward the Allies and against the Central powers for some time. In 1917, Germany, determined to win its war of attrition against the Allies, announced the resumption of unrestricted warfare in war-zone waters. Three days later, the United States broke diplomatic relations with Germany, and just hours after that the American liner Catatonic was sunk by a German U-boat.