The Berlin Blockade was Oa, a barrier erected by Allied forces in postwar Berlin to shield them from angry protests of starving residents. Ob. the Soviet Union's reaction to the establishment of a separate currency in the western occupied zones. Oc. a temporary defensive measure by the United States that was soon taken down. d. a means for the United States to justify its threat to mobilize Allied forces stationed in Turkey. Oe. erected because the United States threatened to invade the Soviet Union.