After the outbreak of the Russian February Revolution in 1917, the first organised strikes erupted in German armament factories in March and April, with about 300,000 workers going on strike. The strike was organized by a group called the Revolutionary Stewards ( Revolutionäre Obleute ), led by their spokesman Richard Müller . The group emerged from a network of left-wing unionists who disagreed with the support of the war that came from the union leadership.  The American entry into World War I on 6 April 1917 threatened further deterioration in Germany's military position. Hindenburg and Ludendorff had called for an end to the moratorium on attacks on neutral shipping in the Atlantic, which had been imposed when the Lusitania , a British ship carrying US citizens, was sunk off Ireland in 1915. Their decision signaled a new strategy to stop the flow of US materiel to France to make a German victory (or at least a peace settlement on German terms) possible before the United States entered the war as a combatant. The emperor tried to appease the population in his Easter address of 7 April by promising democratic elections in Prussia after the war, but lack of progress in bringing the war to a satisfactory end dulled its effect. Opposition to the war among munitions workers continued to rise, and what had been a united front in favour of the war split into two sharply divided groups.