Jan. 31 (UPI) -- On this date in history: In 1917, Germany announces it will wage unrestricted submarine warfare against all ships, including passenger carriers, in war-zone waters. In 1929, the Soviet Union expelled communist revolutionary Leon Trotsky . He was assassinated in Mexico in August 1940. In 1945, U.S. Army Pvt. Eddie Slovik, 24, was executed by firing squad for desertion. His was the first U.S. execution for desertion since the Civil War and the only one to take place during World