(A) the Sussex Pledge
(B) the interception of the Zimmerman telegram
(C) the sinking of the Lusitania
(D) ** unrestricted submarine warfare
EXPLANATIONS BELOW
Concept note-1: -Blockades, part of economic warfare, had been employed throughout history. The Allied blockade (1914-1919), which aimed to prevent war supplies reaching Germany, ultimately also targeted the civilian population. It had its counterpart in the German attempt to block supplies to the Entente.
Concept note-2: -On 4 February 1915, Germany declared a war zone around Britain, within which merchant ships were sunk without warning. This ‘unrestricted submarine warfare’ angered neutral countries, especially the United States.
Concept note-3: -The Blockade of Germany, or the Blockade of Europe, occurred from 1914 to 1919. The prolonged naval blockade was conducted by the Allies during and after World War I in an effort to restrict the maritime supply of goods to the Central Powers, which included Germany, Austria-Hungary and the Ottoman Empire.
Concept note-4: -One U-boat would shadow a convoy and summon others by radio, and then the group would attack, generally on the surface at night. These tactics succeeded until radar came to the aid of the escorts and until convoys could be given continuous sea and air escort all the way across the Atlantic in both directions.
Concept note-5: -Schlieffen’s strategy assumed that Russia, having recently lost the Russo-Japanese War, would take at least six weeks to mobilize its troops and attack Germany from the East. In that time, Germany would stage an attack on France by marching west through neutral territory of the Netherlands and Belgium.