For the same reason that most everybody when they are cornered, fight back.
I’m finishing off John J. Mearsheimer’s classic, The Tragedy of Great Power Politics:
The indictment against Japan for overexpansion boils down to its decision to start a war with the United States, which had roughly eight times as much potential power as Japan in 1941 (see Table 6.2) and went on to inflict a devastating defeat on the Japanese aggressors.
It is true that Japan had picked fights with the Red Army in 1938 and 1939 and lost both times. But as a result, Japan stopped provoking the Soviet Union and the border between them remained quiet until the last days of World War II, when Japan’s fat e was clearly sealed. It is also true that Japan invaded China in 1937 and became involved in a lengthy war that it was unable to win. However, not only was Japan reluctantly drawn into that conflict. but its leaders were confident that China, which was hardly a formidable military power at the time, would be easily defeated. Although they were wrong, Japan’s failure to win a victory in China was hardly a catastrophic failure. Nor was the Sino-Japanese War the catalyst that put the the United States on a collision course with Japan.137 American policymakers were clearly unhappy about Japanese aggression in China, but the United States remained on the sidelines as the war escalated. In fact, it made little effort to help China until late 1938, and even then it offered the beleaguered Chinese only a small package of economic aid.
Two stunning events in Europe-the fall of France in June 1940 and especially Nazi Germany’s invasion of the Soviet Union in June 1941-drove the United States to confront Japan, and eventually led to Pearl Harbor. As Paul Schroeder notes, “The United States did not seriously consider stopping the Japanese advance by force of arms, or consider Japan as an actual enemy, until the Far Eastern war had become clearly linked with the far greater (and, to the United States, more important) war in Europe.” In particular, it was “opposition to Hitler which began to condition American policy in the Far East more than any other factor.”
The Wehrmacht’s victory in the west not only knocked France and the Netherlands out of the war, but it also forced a badly weakened United Kingdom to concentrate on defending itself against a German assault from the air and the sea. Since those three European powers controlled most of Southeast Asia, that resource-rich region was now an open target for Japanese expansion. And if Japan conquered Southeast Asia, it could shut down a considerable portion of the outside aid flowing into China, which would increase Japan’s prospects of winning its war there. And if Japan controlled China and Southeast Asia as well as Korea and Manchuria, it would dominate most of Asia. The United States was determined to prevent that outcome, and thus in the summer of 1940 it began working hard to deter further Japanese expansion.
Japan was anxious to avoid a fight with the United States, so it moved cautiously in Southeast Asia. By the early summer of 1941, only northern Indochina had come under Japan’s control, although Tokyo had been able to get the United Kingdom to shut down the Burma Road between July and October 1940 and the Dutch to provide Japan with additional oil. It seemed by mid-June 1941 that “even if there were little hope of real agreement” between Japan and the United States, “there remained a chance that some kind of temporary and limited settlement might be reached.”’41 At the time, it did not seem likely that they would be at war in six months.
Germany’s invasion of the Soviet Union on June 22, 1941, however, fundamentally altered relations between Japan and the United States and sent them hurtling down the road to war. 142 Most American policymakers, as noted, believed that the Wehrmacht was likely to defeat the Red Army, thus making Germany the hegemon in Europe. A Nazi victory would also have left Japan as the hegemon in Asia, since the Soviet Union was the only great power with an army in Asia that could check Japan.143 Thus, if the Soviets lost to the Germans, the United States would have found itself confronting hostile hegemons in Asia as well as Europe. Not surprisingly, the United States was bent on avoiding that nightmare scenario, which meant that the Soviet Union had to survive the German onslaught of 1941 as well as any future German offensives.
Unfortunately for Japan, it was in a position in 1941 to affect the Soviet Union’s chances for survival. In particular, American policymakers were deeply worried that Japan would attack the Soviet Union from the east and help the Wehrmacht finish off the Red Army. Not only were Germany and Japan formally allied in the Tripartite Pact, but the United States had abundant intelligence that Japan was considering an attack on the beleaguered Soviet Union, which Japan had fought against just two years earlier.
To preclude that possibility, the United States put tremendous economic and diplomatic pressure on Japan in the latter half of 1941. The aim, however, was not simply to deter Japan from striking the Soviet Union, but also to coerce Japan into abandoning China, Indochina, and possibly Manchuria, and more generally, any ambition it might have to dominate Asia. 14s In short, the United States employed massive coercive pressure against Japan to transform it into a second-rate power.
The United States was well-positioned to coerce Japan. On the eve of World War It Japan imported 80 percent of its fuel products, more than 90 percent of its gasoline, more than 60 percent of its machine tools, and almost 75 percent of its scrap iron from the United States.146 This dependency left Japan vulnerable to an American embargo that could wreck Japan’s economy and threaten its survival. On July 26, 1941, with the situation going badly for the Red Army on the eastern front and Japan having just occupied southern Indochina, the United States and its allies froze Japan’s assets, which led to a devastating full-scale embargo against Japan.147 The United States emphasized to Japan that it could avoid economic strangulation only by abandoning China, Indochina, and maybe Manchuria.
The embargo left Japan with two terrible choices: cave in to American pressure and accept a significant dimunition of its power, or go to war against the United States, even though an American victory was widely agreed to be the likely outcome.148 Not surprisingly, Japan’s leaders tried to cut a deal with the United States in the late summer and fall of 1941.
They said that they would be willing to evacuate their troops from Indochina once a “just peace” was reached in China, and they maintained that they would be willing to pull all Japanese troops out of China within twenty-five years after peace broke out between China and Japan.149 But U.S. policymakers stuck to their guns and refused to make any concessions to the increasingly desperate Japanese .I SO The United States had no intention of allowing Japan to threaten the Soviet Union either in 1941 or later in the war. In effect, the Japanese would be defanged either peacefully or by force, and the choice was theirs.
Japan opted to attack the United States, knowing full well that it would probably lose, but believing that it might be able to hold the United States at bay in a long war and eventually force it to quit the conflict. For example, the Wehrmacht, which was outside the gates of Moscow by November 1941, might decisively defeat the Soviet Union, thus forcing the United States to focus most of its attention and resources on Europe, not Asia.
Furthermore, the U.S. military, a rather inefficient fighting machine in the fall of 1941 , might be further weakened by a surprise Japanese attack. Capabilities aside, it was not certain that the United States had the will to fight if attacked. After all, the United States had done little to stop Japanese expansion in the 1930s, and isolationism was still a powerful ideology in America. As late as August 1941 , an extension of the one-year term of service for those who were drafted in 1940 passed the House of Representatives by only one vote.
But the Japanese were not fools. They knew that the United States was more likely than not to fight and likely to win the ensuing war. They were willing to take that incredibly risky gamble, however, because caving in to American demands seemed to be an even worse alternative. Sagan puts the point well: “The persistent theme of Japanese irrationality is highly misleading. . . . [T]he Japanese decision for war appears to have been rational. If one examines the decisions made in Tokyo in 1941 more closely, one finds not a thoughtless rush to national suicide, but rather a prolonged, agonizing debate between two repugnant alternatives.”