America formally entered the Second World War because of one dramatic event – the Japanese attack on the US navy base at Pearl Harbour on 7 December 1941. The nature of the surprise attack, conducted whilst the Japanese were still in discussions with the USA, outraged the Americans.

'Always will we remember the character of the onslaught against us,’ said President Roosevelt on 8 December. ‘No matter how long it may take us to overcome this premeditated invasion, the American people, in their righteous might, will win through to absolute victory.’

But whilst the catalyst for war between America and Japan is clear, the origins of the Japanese decision to attack the USA are both lengthy and murky. Though it was the Japanese entry into southern Indo-China in July 1941 that precipitated the particular crisis that led to war, the roots of the conflict were much deeper and rested to a large extent on Japanese dealings with another country altogether – China.

In the early 1930s Japanese right wing politicians, together with the military elite, managed to side-line many of the burgeoning Western-looking elements within the Japanese governing class. These pro-Western Japanese had enthusiastically adopted Western ways since the accession to the throne of the Emperor Meiji in 1867, and the right wing in Japan despised them and their attempt to curry favour with nations like America and Britain.

However, the Japanese right wing and military elite did not reject one Western value – the belief in the importance of an ‘Empire’ for any country of standing in the world. And by the early 1930s the Japanese had managed to accumulate as ‘colonies’ both Korea and Taiwan as well as various island groups in the Pacific. But now some Japanese wanted to subjugate China, the biggest prize of all.

Just like the Nazis, many Japanese believed that the difficulties their nation faced could only be solved by obtaining more ‘living space’ in neighboring countries. ‘At the time the problem was our population was increasing,’ said Masatake Okumiya, a senior member of the Imperial Navy during WW2, ‘and our natural resources couldn’t sustain the increase. Ideally we hoped to receive co-operation from other countries to solve the problem, but back then the world was under the control of the West and a peaceful solution seemed impossible.'

In September 1931 Japanese military units moved into Manchuria on the Chinese mainland and claimed this land as a new colony. Many in the West were outraged, and Japan withdrew from the League of Nations, complaining about the ‘hypocrisy’ of those Western nations who had the benefit of colonies, but would not allow Japan to join their ‘club’.

Then, in July 1937, the Japanese Imperial Army moved into China proper, reaching Nanking (then China’s capital) in December 1937. The atrocities the Japanese committed in China - infamously in Nanking - are well documented and further angered many in the West.

Japan made a formal alliance with the Nazis and with Mussolini’s Italy on 27 September 1940 – the Tripartite pact. The motivation for the Japanese to join with the two European Fascist countries was clear. Germany had just conquered France and Holland and so, as far as the Japanese were concerned, Dutch and French colonies in Asia seemed ripe for the picking. Indeed, five days before the Tripartite pact had been signed, the Japanese had moved into the northern part of French Indo-China. And then, in July of the following year, they advanced into the southern half of Indo-China.

By the summer of 1941, Roosevelt had decided that America should not stand by and let Japanese aggression run unchecked.

The American government announced in July 1941 that all Japanese assets in the USA would be frozen and that there would be an embargo on selling key raw materials to Japan – including oil. It was obvious to everyone that without oil from America the Japanese industrial infrastructure would suffer hugely – almost catastrophically. Japan itself possessed virtually none of the raw materials necessary to fuel a modern state.

And so the two countries were now set on a course of considerable conflict. One of them would have to compromise or else the situation would only escalate. And it is in this context that both sides misjudged the other. Within the American leadership, for example, there was clearly a sense of massive over-confidence. ‘I think the feeling in the United States was that Japan could never defeat us,’ says Professor Dallek. ‘How could they possibly defeat the United States? We are such a larger power, we have such industrial potential. Would they be so foolish as to attack us, to go to war with us? We’ll mop them up and they can’t really fight all that effectively. So we have to take a tough line with them. American public opinion wants it and Congress is happy to see this happen. Take a tough line with them and it’s not going to lead to war. That, I think, is the perspective of the time, though of course it was absolutely wrong.’

The United States, having announced the trade embargo, then linked the Japanese aggression in southern Indo-China, which had precipitated the crisis, with the larger and seemingly intransigent problem of the Japanese war in China. This was to culminate in a demand from Secretary of State Cordell Hull in November 1941 that any settlement with the Japanese was conditional on an agreed withdrawal of Imperial Forces from China. Even though this demand may have simply been a negotiating ploy, it was always going to prove virtually impossible for the Japanese to agree to leave China given how much prestige they had invested in the attempted conquest of the country.

Throughout the summer and autumn the Japanese considered their options. And then, on 6 September, at an Imperial Conference in Tokyo, a radical plan was proposed - the brain child of the brilliant and charismatic naval commander, Admiral Isoroku Yamamoto. He argued that the Imperial Navy should launch a surprise attack against the US Pacific fleet at Pearl Harbour in Hawaii and then sue for a compromise peace. ‘America is a big country and we knew that we wouldn’t be able to win against them once the war was prolonged,’ says Masatake Okumiya, explaining Japanese logic. ‘But at the time the fleet was the mainstay of military power, be it American, British or Japanese. The fleet represented a nation’s military power. So if you destroyed the fleet the damage would be huge. It would ruin President Roosevelt’s reputation as a commander-in-chief and he might then be put in a difficult situation.’

It was to prove a catastrophic misjudgement. ‘I think that this shows the extent of the Japanese self complacency,’ says Professor Akira Iriye. ‘They really did not know much about the United States - or other countries for that matter - and they did not know much about China. I mean this is their island mentality… they really had not studied other nations or anything like that, they’ve been so very self centred, there’s no question about that.’

Emperor Hirohito, who had ascended to the Imperial throne in 1926, confided his doubts about the wisdom of the impending war at the conference held in September 1941. But, typically, these were expressed elliptically – indeed, partly in the form of a poem. But Hirohito was more than a mere bystander to events. He could have chosen to act differently, with decisiveness. But he didn’t. He had never, for example, openly condemned the atrocious actions of Imperial troops in China.

And so events took on a momentum of their own, with the Japanese fleet setting sail for Pearl Harbour on 26 November. Meantime, negotiations were still proceeding in a desultory fashion in Washington. The Japanese had offered to leave Indo-China but had made little concessions on the question of China itself. Then, on 6 December, President Roosevelt sent a telegram to the Japanese Emperor. This message, says Professor Iriye, appealed ‘to the Emperor to wind back the clock, so to speak, to do something about preserving the peace between two countries. If that telegram had reached the Emperor before the attack had taken place that would have been a very interesting moment in which one could really talk about the clear responsibility for the Emperor for or against war. But the cable got into the hands of the Japanese army apparently, and so the Emperor saw the telegram only after he had signed the declaration of war and it came too late - the army sabotaged the whole process.’

Thus, on the morning of Sunday 7 December, Japanese warplanes attacked Pearl Harbour. But this was certainly not to be the devastating blow against the United States that the Japanese leadership had hoped for. For though several large warships were sunk or damaged, the American aircraft carriers were all out at sea.

However, Pearl Harbour was undoubtedly a humiliation for the Americans, especially given the fact that American code-breakers had cracked key Japanese ciphers. But it was also, according to Professor Dallek, a ‘god-send’ for President Roosevelt: ‘not because he contrived it, it was a genuine surprise’ but because it allowed the United States to enter the war in a united fashion.

Though Pearl Harbour may have been a ‘god-send’ for Roosevelt, it was a disaster for the Japanese leadership – indeed for the whole Japanese nation. ‘It mobilises American opinion,’ says Professor Iriye. ‘Even isolationists who had been opposed to US intervention in Europe all now say that this was a humiliating cheap shot against the United States and that now the nation must unite and fight against this treachery.’

For the rest of the war, the battle cry of US Marines would be: ‘Remember Pearl Harbour!’

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