Japan's imperial expansion in Asia in the 1930s set the stage for war with the US.

Before World War II, the US was a Pacific power

Decades before Pearl Harbor, the US held major Pacific territories—Hawaii, the Philippines, Guam, American Samoa, and numerous island bases—giving it strategic reach across the western Pacific. This presence increasingly overlapped with Japan’s imperial ambitions in the region, contributing to rising tensions.

Japan attacked Pearl Harbor largely because it was running out of oil

This video traces how US-led sanctions and Japan’s near-total dependence on imported oil pushed Japanese leaders toward a high-risk plan: seize Southeast Asian oil fields and neutralize the American Pacific Fleet, hoping Washington would negotiate rather than fight.

The US asked Japan to leave China less than two weeks before Pearl Harbor

On Nov. 26, 1941, Secretary of State Cordell Hull issued a note calling on Japan to withdraw from China and Indochina—terms Tokyo saw as impossible. The note confirmed to Japanese leaders that diplomacy had collapsed, accelerating plans for the Pearl Harbor strike (which had been formally approved Nov. 5).

Hitler declared war on the United States four days after Pearl Harbor

Despite having no treaty obligation to join Japan’s fight, Hitler declared war on the US on Dec. 11, 1941. The move pulled America into the European theater and is widely seen as one of Hitler’s most strategic blunders.

The US Pacific strategy sought control of key islands to close in on Japan

The US adopted a two-pronged "island hopping" campaign across the Central and Southwest Pacific from 1943–44, deliberately targeting strategically crucial but less-defended islands. This allowed forces to bypass heavily fortified Japanese strongholds and build airfields for bombers aimed at Japan, drastically accelerating the path toward Tokyo while conserving manpower and resources.

The US used military pressure to force Japan to open to foreign trade in the 1850s

Commodore Matthew Perry arrived in Edo Bay (now Tokyo Bay) with heavily armed warships, pressuring Japan to open its ports. His expeditions led to the 1854 Treaty of Kanagawa, which opened two ports for supplies and established formal US-Japan relations. Full commercial trade followed later under the 1858 Harris Treaty.

Before Pearl Harbor, the US was a nonbelligerent ally to the Allied powers

Between September 1940 and December 7, 1941, the United States remained officially neutral—yet President Roosevelt incrementally shifted policy from “cash‑and‑carry” to Lend‑Lease, funneling critical military aid to Britain and other allies without entering the war.

Japan had the world's best carrier aviation in 1941

In late 1941, Japan possessed the world’s most powerful carrier fleet and the best-trained naval aviators, giving it a short-term edge over the US. But Japan couldn’t replace ships or pilots quickly, and US industry would soon outbuild it.

The attacks prompted a quick jump in American public support for war

In a Gallup poll taken days after the attack, an extraordinary 97% of Americans approved Congress declaring war on Japan—reflecting overwhelming national unity in the wake of the strike.

Okinawa’s ferocity convinced the US atomic bombs was necessary

The brutal 82-day Battle of Okinawa—where US forces suffered nearly 50,000 casualties and Japanese military and civilians lost over 200,000 lives—clinched the grim reality that a full invasion of Japan would be even bloodier. This stark lesson directly shaped American decisions to deploy atomic weapons, aiming to avoid a potentially catastrophic ground war on the Japanese mainland.

The Battle of Midway flipped the balance of power in Pacific naval dominance

Between June 4–7, 1942, U.S. carrier-based aircraft, aided by broken Japanese codes and radar detection, ambushed and sank all four Japanese fleet carriers while losing only one, decisively undermining Japan's offensive capacity and marking the turning point in the Pacific War.

Japan committed mass war crimes during its invasion of China

During the 1937 invasion, Japanese forces carried out systematic atrocities—including mass executions, rape, torture, forced labor, and chemical warfare. The Nanjing Massacre alone killed tens of thousands over a span of six weeks, with some estimates claiming 300,000.

The Pearl Harbor attack led to the mass internment of Japanese Americans

In the months after Pearl Harbor, the US forcibly removed and incarcerated about 120,000 Japanese Americans—two-thirds of them citizens. Driven by fear and racism, the policy is now recognized as a grave violation of civil rights.

Japan was an empire from 1868 until 1947

The Empire of Japan began on Jan. 3, 1868, and facilitated rapid modernization. It endured through a period of colonial expansion—including Korea and Taiwan—1930s militarism, and participation in WWII, until Japan’s formal transformation into a constitutional state under the 1947 constitution following Allied occupation.

Japan's attack on Pearl Harbor caused heavy losses but failed to cripple the US navy

Japan’s air assault sank or damaged 18 warships (including eight battleships) and destroyed 188 aircraft, killing 2,403 Americans, yet all three Pacific Fleet aircraft carriers were absent and survived, and vital infrastructure like oil depots and repair yards remained intact—preserving core US naval power and enabling a rapid recovery. Watch original reporting here.

How the US entered WWI in 1917

Originally taking a position of neutrality during the course of World War I, the United States of America eventually relented. Entering the war in 1917, support for the British and French had risen and Americans were incensed by Germany's overtures to Mexico and U-boat attacks that sank ships and ended American lives. See how and why the US entered WWI in this article.

US intelligence failures contributed to the success of the Japanese attack

Despite breaking Japan’s diplomatic codes, US agencies failed to integrate warnings, successfully track Japan’s carriers, or even believe a Hawaii strike was possible (they also had not cracked Japan’s naval codes). Missed signals, ignored reports and poor coordination led to one of the worst intelligence failures in US history.

Japan's 1990s deflation followed the country's fastest growth period

The end of World War II ended Japan's isolation in the global economy, prompting what's now called the "Japanese Economic Miracle." From the 1940s to the 1980s, Japanese policy makers enacted ultra-loose monetary policies that pushed a ton of cash into the market and fueled rapid growth. But these policies ultimately helped create a bubble and sent the country into a deep period of deflation.

What happened to Americans who were in Japan during Pearl Harbor?

When Japan bombed Pearl Harbor in December 1941, roughly 10,000 American civilians were stranded in Japanese-occupied territory. Tense diplomatic negotiations eventually secured two prisoner exchanges conducted via ship across 20,000 nautical miles to return nearly 3,000 Allied civilians, while Japanese Americans in North and South America were sent in the opposite direction, many to a country they had never called home.

The attack at Pearl Harbor required nearly a year of planning and preparation

In early 1941, Admiral Isoroku Yamamoto ordered detailed planning for a surprise carrier strike on Pearl Harbor. Japanese teams spent months refining torpedo modifications, training pilots, and rehearsing the complex attack.

Wartime conferences exposed cracks in the US–Soviet alliance

At the Tehran, Yalta and Potsdam Conferences, Allied leaders coordinated WWII strategy—but deep disagreements over postwar Europe foreshadowed the Cold War. The USSR’s push for influence in Eastern Europe clashed with US and British calls for self-determination.

See a visualization of the Japanese attack on Pearl Harbor.

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Learn how Japan used the jet stream to launch attacks on US soil during World War II

In the final two years of the war, over 9,000 Fu-Go balloon bombs were launched from Japan, with about a thousand estimated to have reached North America. Six civilians killed by a Fu-Go bomb in Bly, Oregon, on May 5, 1945, became the only known deaths on American soil by enemy action during the war.

The Pearl Harbor attack was influenced by a British raid on Italian battleships

Japan closely studied Britain’s 1940 attack at Taranto, where carrier-launched torpedo planes crippled Italian battleships in shallow water. Although Japanese planning for Pearl Harbor was already underway, Taranto demonstrated the plan’s feasibility and strengthened Japanese confidence that a surprise carrier assault could cripple the US Pacific Fleet.

World War I brought attention to US reliance on mineral imports

Domestic stockpiles were inadequate for the extended trade disruptions caused by the four-year war. In response, the US Geological Survey increased its geological mapping to help search for important metals alongside new oil fields for fuel.

The Flying Tigers: American fighter pilots who fought for China in WWII

Read the story of the Flying Tigers, a unit of American pilots, many Chinese-Americans, hired by the Chinese in 1941 to fight the Japanese in the skies. While the US wasn't officially at war with Japan until later on, some of the earliest American "victories" over the Japanese were won by the Flying Tigers. Read more of this amazing bit of aviation history here.

The UK was already in a depression before the US Great Depression took hold

The US Great Depression was felt globally, but the severity and length of different countries’ economic downturns varied. For instance, Japan was the first country to exit its depression.

US–Soviet hostility began long before the Cold War

US–Soviet tensions began decades before WWII. After the 1917 revolution, the US refused to recognize the Bolshevik regime and even sent troops to fight against it.

The Japanese Navy used radio silence and deception to mask its approach

In late November 1941, Japan’s carrier strike force maintained total radio silence while operators back home broadcast normal traffic—creating ambiguity about the location of the fleet. The deception obscured US intelligence and helped create a surprise attack.

See what it was like to live in the United States during World War II

In America, life was transformed by total war: sixteen million service members left civilian life, while massive industrial production demanded labor. Women, minorities, and teens filled factories, fueling boomtown growth and breaking social barriers. Simultaneously, rationing, recycling drives, Victory Gardens, ration stamps, blackout drills, and war bond campaigns permeated daily routines.

The Great Depression was an international depression felt far beyond the US

Many countries suffered through a depression in the 1930s that the First World War, the US stock market crash, and an economic downturn in Germany turned into an international crisis.

Should the US have entered into World War I?

America entered World War I in 1917, but had remained neutral until that point. President Woodrow Wilson addressed Congress, further underlining the USA's neutrality. Eleven weeks later, he asked for a declaration of war. With attacks by German saboteurs on an American munitions depot, it seemed he had no choice. But did he? This article asks what might have happened if the US stayed out of WWI.

President Polk deliberately provoked war with Mexico

After Mexico refused to sell California and New Mexico, President James K. Polk ordered US troops into disputed territory between the Nueces River and the Rio Grande—knowing it would likely spark a conflict. When fighting broke out, he used it to justify declaring war.

Roosevelt’s post-Pearl Harbor address became one of America’s most iconic speeches

Delivered to a joint session of Congress on Dec. 8, 1941, President Franklin D. Roosevelt declared Dec. 7 “a date which will live in infamy.” The speech, heard by tens of millions of Americans, helped consolidate national support for entering the war.

At one point, the land underneath the Imperial Palace in Japan was reportedly worth more than California

Before Japan's economy crashed and sent the country into two decades of deep deflation, the real estate market was experiencing euphoric highs. The Imperial Palace never actually went on the market, so it's difficult to actually compare the value to California.

In the 1930s, Congress nearly passed a constitutional amendment requiring a national vote before declaring war

The Ludlow Amendment, proposed amid rising isolationism after World War I, would have required a national referendum before Congress could declare war, except in cases of direct attack. It was defeated 209 to 188 in 1938 after Roosevelt lobbied against it.

A trade war is an economic conflict where nations impose tariffs or other trade barriers on each other in retaliation for similar actions.

How two US Presidents defined WWII and its aftermath

The National WWII Museum’s “To the Best of My Ability” podcast series delves into how Presidents Franklin D. Roosevelt and Harry S. Truman steered the US through World War Two.

The Roosevelt Corollary transformed the Monroe Doctrine from a defensive warning into a rationale for US military intervention

In 1904, President Theodore Roosevelt declared that the US had the right to exercise international police power in Latin America. Over the following two decades, the US intervened militarily in the region about a dozen times—often enough that Marines became known locally as "State Department troops."