7.13 World War II: Military

TLDR

Japan's attack on Pearl Harbor brought the United States into World War II, with campaigns against Germany in Europe and Japan in the Pacific. Germany and Japan surrendered, while Allied leaders made plans for postwar peace.

What to Know About World War II

• Japan's expansion and American embargoes strained relations before the attack on Pearl Harbor; the US declared war on Japan, and Germany and Italy then declared war on the US.
• Nazi Germany murdered six million Jewish people and millions of others, while US immigration restrictions limited Jewish refugees and the War Refugee Board began rescuing people late in the war.
• The US and Britain prioritized defeating Germany, opened a second front with the Normandy invasion, and accepted Germany's surrender in May 1945.
• In the Pacific, US forces used island-hopping to approach Japan; thousands died on the Bataan Death March, and kamikaze attacks inflicted major damage at Okinawa.
• Truman chose to use atomic bombs, viewing them as a way to save American lives; the US bombed Hiroshima and then Nagasaki.
• Military service gave women and minorities chances to improve their socioeconomic standing during the war, and it also sparked debate over racial segregation in the armed forces.
• At Casablanca, Roosevelt and Churchill demanded Axis unconditional surrender; at Yalta, the Big Three planned Soviet entry into the war against Japan and a new world peace organization.

Pre-War Japanese Aggression

US relations with Japan became increasingly strained as Japan invaded China and expanded into Southeast Asia. Those tensions, combined with American embargoes and failed diplomacy, led to the attack on Pearl Harbor and full US entry into World War II.

When Japan joined the Axis, FDR responded by prohibiting the export of steel and scrap iron to all countries except Britain and the nations of the Western Hemisphere. After Japan invaded French Indochina, FDR froze all Japanese credits in the US and cut off access to key materials, including US oil.

Attack on Pearl Harbor. Getty Images

Naval intelligence experts had broken the Japanese diplomatic code and were intercepting and reading all messages between Tokyo and the Japanese embassy in Washington. To mask war preparations, Japan sent another envoy to Washington with new peace proposals. Code breaking allowed American diplomats to know that Japanese terms were unacceptable even before they were formally presented.

Attack on Pearl Harbor

Diplomatic negotiations between the United States and Japan broke down in late 1941. When officials in Washington realized conflict was imminent, they sent warning messages to American bases in the Pacific, but these warnings failed to arrive in time.

On December 7, 1941, at 7:55 AM Hawaii time (just before 1 PM in Washington):

• Japanese carrier-based aircraft launched a surprise attack on the U.S. Navy base at Pearl Harbor
• In little more than an hour, the attack devastated the American Pacific fleet
• 20 American warships were damaged or sunk, including all eight battleships present
• More than 2,400 American service members and civilians were killed
• An additional 1,200 were wounded

The following day, President Roosevelt addressed Congress, calling December 7th "a date which will live in infamy," and requested a declaration of war against Japan. Congress approved with only one dissenting vote. On December 11, Germany and Italy declared war on the United States, bringing America fully into World War II on both fronts.

As the war progressed, Americans became increasingly aware of Japanese war atrocities, including the Rape of Nanking in China, where tens of thousands of civilians were massacred. These revelations strengthened American resolve and contributed to the framing of the war as a fight against barbarism and tyranny. Many Americans saw the war as a fight to keep freedom and democracy alive against fascist and militarist ideologies.

The Holocaust and American Response

Among the most horrific discoveries of the war was the systematic genocide perpetrated by Nazi Germany. The Holocaust (also known as the Shoah) was the state-sponsored murder of six million Jewish people and millions of others deemed "undesirable" by the Nazi regime, including Roma people, people with disabilities, LGBTQ individuals, political opponents, and others.

The American government's response to the Holocaust was complex and, in many ways, inadequate:

• Early reports of Nazi atrocities reached the United States by 1942, but the full scale of the genocide was difficult for many Americans to comprehend
• Prevailing anti-Semitism and strict immigration quotas established in the 1920s limited the number of Jewish refugees allowed into the United States
• The War Refugee Board, established by Roosevelt in 1944, helped rescue thousands of Jews but came late in the war
• Military leaders prioritized winning the war quickly over specific humanitarian interventions, arguing that defeating Germany was the fastest way to end the genocide

American soldiers were among the first Allied troops to liberate Nazi concentration camps in 1945. Their eyewitness accounts and photographs provided irrefutable evidence of Nazi atrocities. The liberation of camps like Buchenwald and Dachau profoundly affected American soldiers and the public, strengthening the moral case for the war and influencing American support for the creation of the United Nations and the State of Israel.

The failure to do more to rescue European Jews remains a painful chapter in American history. The Holocaust demonstrated the devastating consequences of hatred and indifference, and its legacy continues to inform discussions about America's moral responsibilities in the face of genocide and human rights abuses around the world.

The European Theater

The US and Britain achieved a close wartime partnership. The cooperation between Roosevelt and Churchill ensured a common strategy. Allied cooperation was one reason for victory. Advances in science and technology, such as the Manhattan Project, and the contributions of servicemen and women also helped secure military success. They decided from the outset that Germany posed a greater danger and thus gave priority to the European theater.

The US favored an invasion across the English Channel. Army planners led by Chief of Staff George C. Marshall and his protégé, Dwight D. Eisenhower, were convinced that this would be the quickest way to win the war. The British, remembering trench warfare and hoping to protect India, their most important colony, preferred a perimeter approach with air and naval attacks around the continent. As a result, they began by taking back Africa and then moved into Europe via Italy.

General George Patton quickly rallied the troops, and by May of 1943, the Germans were driven from Africa.

The long-awaited second front finally came on June 6, 1944. For two years, the US and Britain had focused on building an invasion force of nearly 3 million troops and a vast armada of ships and landing craft to carry them across the English Channel. Eisenhower hoped to catch Hitler by surprise and chose the coast of Normandy, which was less heavily fortified than the Pas-de-Calais, though the lack of good harbors there meant the Allies had to build artificial Mulberry harbors.

D-Day was originally set for June 5, but bad weather forced a delay. On June 6, the invasion began.

• The night before, three divisions parachuted behind the German defenses
• At dawn, British and American troops fought their way ashore
• By the end of the day, Eisenhower had secured his beachhead

American tanks raced across the countryside and liberated Paris by the end of August.

The end came quickly as a massive Russian offensive swept toward Berlin, while American and British forces advanced from the west.

The Allied air force began firebombing German cities such as Hamburg and Dresden, as well as Tokyo in Japan. This was done with high-explosive, incendiary, phosphorous, and napalm bombs. The resulting firestorm was so powerful that buildings erupted in flames over 20 feet high. With hurricane-force, 150-mile-per-hour winds were sucked into the oxygen vacuum created by the fire, ripping trees out by their roots, collapsing buildings, and pulling children from their mothers' arms.

Eight square miles of the city center burned in an inferno that raged for hours. The temperature in the firestorm reached 1,400 degrees Fahrenheit. There was no oxygen to breathe; anything flammable burst spontaneously into flame.

By April, the armies had surrounded Berlin. Hitler refused to call for retreat or surrender. He ordered all males, from toddlers to elderly men, to fight or be shot on the spot. Hitler committed suicide on April 30. A week later, on May 7, Eisenhower accepted the unconditional surrender of German forces.

The Pacific Theater

The war in the Pacific was dominated by naval forces battling over vast areas. After taking back Midway, the US conducted amphibious “island-hopping” campaigns—retaking one island after another to move closer to Japan—rather than attempting to reconquer the Dutch East Indies, Southeast Asia, and China.

In early 1942, the Japanese conquered the Philippines. The American-Filipino forces on the main island fell back toward the Bataan Peninsula, were besieged, and ultimately surrendered in May 1942. When General Douglas MacArthur, commander of army units in the South Pacific, was driven from the islands, he famously vowed, “I shall return.” Japanese atrocities began at the very beginning of the occupation. The captured Americans and Filipinos were marched from Bataan with little food, water, or rest. Coupled with rampant violence, between 7,000 and 10,000 died on what became known as the Bataan Death March.

Kamikaze (Japanese suicide planes) inflicted major damage in the colossal Battle of Okinawa. Before succeeding in taking this island near Japan, US forces suffered 50,000 casualties.

Atomic Bomb

The defeat of Japan was now only a matter of time. The US had three possible ways to proceed. The decision now fell to Harry S. Truman, as FDR had died just months into his unprecedented fourth term:

• The military favored a full-scale invasion, though casualties would have likely reached into the hundreds of thousands
• Diplomats suggested a negotiated peace, urging the US to modify its unconditional surrender terms to allow Japan to retain its emperor
• The third option involved using the highly secret Manhattan Project

Since 1939, the US had spent $2 billion developing an atomic bomb based on the fission of radioactive uranium and plutonium. Scientists—many of them refugees from Europe—worked to perfect this deadly new weapon at the University of Chicago, Oak Ridge (TN), and Los Alamos (NM).

In the New Mexico desert at the Trinity Site on July 16, 1945, they successfully tested the first atomic bomb, creating a fireball brighter than several suns and a mushroom cloud that rose some 40,000 feet. The desert sand turned to glass.

Truman decided to use this new atomic bomb, viewing it as a way to save hundreds of thousands of American lives.

Weather on the morning of August 6 dictated the choice of Hiroshima as the bomb’s target. Other sites were considered, but much of Japan had already been destroyed by conventional bombing. Hiroshima was an industrial city. The explosion incinerated four square miles and instantly killed 60,000 people. Truman called on Japan to unconditionally surrender or face “utter destruction.”

Two days later, with no response, the US dropped a second bomb on Nagasaki. What the Japanese didn’t know was that this was the last atomic bomb the US had.

Three weeks later, aboard the battleship Missouri with General MacArthur, the Japanese surrendered.

Wartime Conferences

During the war, the Big Three (leaders of the US, Soviet Union, and Great Britain) arranged to confer secretly to coordinate their military strategies and lay the foundation for peace terms and postwar involvement.

Casablanca

In January 1943, Roosevelt and Churchill agreed on the grand strategy to win the war, including the invasion of Sicily and Italy, and the demand for “unconditional surrender” from the Axis powers.

Tehran

The first wartime Big Three conference brought together Roosevelt, Stalin, and Churchill in Tehran, Iran, in 1943. They agreed that Britain and America would begin their drive to liberate France, while the Soviets would invade Germany and eventually join the war against Japan.

Yalta

The Big Three met again in February 1945 at the Yalta Conference. Their agreement would prove the most historic of the three meetings. After victory in Europe, they agreed that:

• Germany would be divided into occupation zones
• There would be free elections in the liberated countries of Eastern Europe (even though Soviet troops controlled the territory)
• The Soviets would enter the war against Japan, which they did just as Japan surrendered
• A new world peace organization (the future United Nations) would be formed at a conference in San Francisco

Potsdam

In late July, after Germany’s surrender, only Stalin remained from the original Big Three. Truman was now US president, and Clement Attlee had replaced Churchill as British prime minister. The three leaders met in Potsdam and agreed:

• To demand Japan’s unconditional surrender
• To hold war-crime trials of Nazi leaders

🎥 Watch: AP US History - World War II