Alternate history: what if Japan hadn't attacked Pearl Harbor?

At the most extreme, no attack on Pearl Harbor could have meant no US entering the war, no ships of soldiers pouring over the Atlantic, and no D-Day, all putting ‘victory in Europe’ in doubt. On the other side of the world, it could have meant no Pacific Theatre and no use of the atomic bomb. This all depends on whether the US would have stayed out of the fight.

The Japanese attack on Pearl Harbor, planned in response to debilitating US economic restrictions, aimed to knock out the Pacific Fleet and crush American morale in one fell swoop. But the plan very possibly could have been shelved.

“Many Japanese leaders, including Admiral Yamamoto Isoroku, were keen to avoid a long war against the United States, conscious of the huge disparity in economic power between the two,” says Robert Cribb, professor in Asian history at the Australian National University. “Their preference was for agreeing [to the US demand] to wind back their presence in China in exchange for a loosening of the embargoes.”

Pearl Harbor podcast series

Member exclusive | Browse and listen to all episodes in our podcast series on the December 1941 attack on Pearl Harbor

Listen to all episodes now

Emperor Hirohito similarly had misgivings about going to war, so Pearl Harbor may just have been spared if he had imposed his will on his government. Without that commitment to pre-emptive military aggression, the imperial leadership may have looked to agree to US demands, but in a “partial, half-hearted and insincere way that was nonetheless sufficient to placate the US”, according to Cribb. If this successfully eased tensions, they could turn their attention to winning the war that had been raging against China since 1937.

“Japan’s practice had always been incremental expansion – Taiwan, then Korea, then the attempt in Siberia, then Manchuria, then slices of north China,” says Cribb. “The Sino-Japanese War was not in their playbook and they hoped to find Chinese partners with whom to sign a peace.” Any kind of deal with the Chinese nationalist government under Chiang Kai-shek may have preserved some of Japan’s interests but, Cribb adds, would have been near to impossible following the 1937 Nanjing Massacre, which had seen the mass killing and ravaging of many thousands of Chinese citizens and capitulated soldiers by the Japanese Imperial Army.

Was war between the US and Japan inevitable?

In truth, the economic restrictions placed on Japan – an embargo on the sale of oil, the freezing of Japanese assets in the US, and the Panama Canal being closed to Japanese shipping – left its empire vulnerable. Supplies of natural resources needed to be secured for any hopes of expansion. With Russia an unlikely option after a recent chastening defeat by the Soviets, the Japanese would always look to Southeast Asia.

Japan occupied French Indochina in 1940 and was targeting the Philippines. But this was a US protectorate, meaning Japan would still come into conflict with the US, even if not at the headquarters of their Pacific Fleet at Pearl Harbor.

Even without the Pearl Harbor attack, the US may have been driven to war by aggression in Southeast Asia

It was not just the US that the Japanese would be taking on. Expanding into Southeast Asia meant facing the British in Burma, Malaysia and Singapore, and the Dutch. “The most useful alternative development for Japan would have been to engineer a coup in the Dutch East Indies [Indonesia],” says Cribb. “It might have given Japan access to crucial oilfields, but such a coup would have been difficult and the US was unlikely to permit the Japanese to bypass the embargoes in that way.”

• The WW2 battle of Okinawa: the bloodiest assault of the Pacific War

Even without the Pearl Harbor attack then, the US may have been driven to war by aggression in Southeast Asia. A deeply antagonistic relationship with Japan had developed in the 1930s, since the invasion of China. “Japan’s great strategic error was to join the Tripartite Pact in September 1940,” states Cribb. “The Pact [forming the Axis Powers with Nazi Germany and Italy] was of no strategic use to Japan, but it had the effect of confirming the US view that Japan was the enemy.”

US President Franklin D Roosevelt recognised the threat of the Axis Powers and was stretching the limits of US neutrality by supporting Britain. Through Lend-Lease, the US supplied weapons, vehicles, food and other resources to help with the war effort, making the country the “arsenal of democracy”. But FDR struggled to convince isolationists that US involvement was imperative.

Without such a shocking attack as Pearl Harbor, winning this support would be more difficult. It is extremely unlikely that a Japanese attack on the Philippines, Dutch East Indies or British-controlled parts of Southeast Asia could provoke the same reaction for revenge. Yet FDR was committing support to the Allied forces and eager to persuade the isolationists that joining the war was essential to US interests, says Cribb. The chances are that the US would still have entered the war, but by a longer road.

• Pearl Harbor: 5 frontline stories from people who were there

If that meant the war went on for longer, then Japan would have faced steadily greater difficulties in maintaining control of Southeast Asia, claims Cribb. The “immense disparity between the US and Japanese economies” would still have given the Americans a key advantage. However, if the war progressed without the attack on Pearl Harbor, the closing stages may still have seen the US and Japan with a shared desire, too – keeping the Soviets’ role at a minimum. As Cribb notes: “The Japanese authorities desperately wanted to avoid being occupied by the Soviets, while the US was keen not to share the occupation.”

Robert Cribb is a professor in Asian history at the Australian National University. He was speaking to freelance writer Jonny Wilkes

This article was first published in the November 2020 edition of History Revealed

Subscribe to BBC History Revealed to get more content like this