Unrestricted submarine warfare was instituted in 1915 in response to the British naval blockade of Germany. Prize rules, which were codified under the 1907 Hague Convention—such as those that required commerce raiders to warn their targets and allow time for the crew to board lifeboats—were disregarded and commercial vessels were sunk regardless of nationality, cargo, or destination. Following the sinking of the on 7 May 1915 and subsequent public outcry in various neutral countries, including the United States, the practice was withdrawn. However, Germany resumed the practice on 1 February 1917 and declared that all merchant ships regardless of nationalities would be sunk without warning. This outraged the U.S. public, prompting the U.S. to break diplomatic relations with Germany two days later, and, along with the Zimmermann Telegram, led the U.S. entry into the war two months later on the side of the Allied Powers.