Public opinion on entering the war became polarized in very complicated ways. Conservatives divided into pro-war ("interventionist") and anti-war ("isolationist") blocs, as did liberals. Republicans split and Democrats split. FDR was the leader of the interventionist liberal Democrats, but he was opposed by old allies like [[John L. Lewis]] and [[Joe Kennedy]], and supported by old foes like [[Henry Stimson]].
In general the dispute was entirely focused on Europe. Virtually every group was hostile to Japan and supported a strong pro-[[Nationalist China ]] policy, which FDR pushed vigorously. Tokyo was threatened: end its invasion of China or the U.S. FDR would--and didat urging of [[KGB]] agent [[Harry Dexter White]] working as an Undersecretary of the Treasury--cut off Japan's oil supplies. Japan responsed responded to an ultimatum--written by Harry White--with a decision for war. Once Pearl Harbor was attacked (Dec. 7, 1941), all the prior divisions vanished overnight, and all groups supported the war effort. Later stories to the effect that FDR knew about the Pearl Harbor attack in advance were all false fabrications.
see [[American Homefront, World War II]]
[[Image:Josephstalin.jpg|thumb|325px|right|Roosevelt in 1941 formed an alliance of convenience with Stalin to defeat Hitler.]]
In August 1939 Stalin made an alliance with Hitler that allowed Hitler to invade under which both jointly waged aggressive war against Poland; the two divided Poland and eastern Europe between them, as Germany turned toward France and Britain. With Roosevelt strongly supporting France and Britain, the American Communist Party began attacking Roosevelt in the wildest terms and did so for the next twenty-two months. In the 1940 election, pro-Moscow elements in the CIO forced [[John L. Lewis]] to turn against Roosevelt and support the liberal Republican [[Wendell Willkie]]. Roosevelt meanwhile moved right, and brought into top jobs the GOP vice presidential nominee from 1936, Frank Knox (a conservative who became Secretary of the Navy) and conservative Republican lawyer [[Henry Stimson]], who took over the War Department. Rejecting advice from the far left, 90% of CIO members voted for Roosevelt, who was easily elected to a third term.
Roosevelt was determined to help Britain and at one point after Pearl Harbor [[Winston Churchill]] even moved into the White House to coordinate war strategy. Isolations, led by the [[America First]] Committee and Senator [[Burton K. Wheeler]] tried to block the moves toward war. [[File:Warplan.jpg|thumb|400px|Wheeler leaks top secret US war plan three days before Pearl Harbor]]