7.13 World War II: Military

8 min readdecember 30, 2022

Robby May

Robby May

Caleb Lagerwey

Caleb Lagerwey

AP US History 🇺🇸

454 resources
See Units

Pre-War Japanese Aggression

US relations with Japan were becoming increasingly strained as a result of Japan’s invasion of China and ambitions to extend its conquests to Southeast Asia.
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. When Japan invaded French Indochina, FDR froze all Japanese credits in the US and also cut off Japanese access to vital materials, including US oil.
The 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

Upon the breakdown of negotiations with the Japanese, officials in Washington immediately sent warning messages to American bases in the Pacific, but they failed to arrive in time. 
At 7:55AM, just before 1PM in Washington, squadrons of Japanese carrier-based planes caught the American fleet at Pearl Harbor totally by surprise. In little more than an hour, they crippled the American Pacific fleet and its major base, sinking 20 warships and killing more than 2400 American sailors and wounding 1200. 
Roosevelt spoke before Congress the next day, calling December 7th “a date which will live in infamy” and asked for a declaration of war on Japan.  Congress acted immediately by declaring war, with only one dissenting vote. On December 11, Germany and Italy declared war against the US, and the nation was now fully involved in WWII.
As the war dragged on, the US learned more and more about the evils perpetrated by the Japanese and Nazis. Americans were horrified to learn about Japanese war crimes of mass rape and murder of civilians in places like Nanjing, China.

America and the Holocaust

In Europe, the US began to learn about Nazi concentration camps, where the Nazis imprisoned and killed those the state considered undesirable, including Jews, Roma people, those with disabilities, LGBTQ people, and others. The Holocaust or Shoah was the systematic killing of Jewish people in Europe by the Nazis, and by the end of the war in 1945, over 6 million Jews and 11 million overall were dead at the hands of the Nazis and their collaborators. 
During the Holocaust, the United States government was aware of the systematic persecution and extermination of Jews and other minority groups by the Nazi regime in Europe. However, the United States did not take significant action to intervene or to provide assistance to those who were being targeted by the Nazis.
One major factor that contributed to the lack of action by the United States was the isolationist sentiment that was prevalent in the country during the 1930s. Many Americans believed that the country should stay out of the conflict and not become involved in the affairs of other nations. This sentiment was reflected in the policies of the government, which prioritized neutrality and non-interference.
Another factor was the limited immigration policies of the United States, which made it difficult for refugees, including Jews, to enter the country. Despite efforts by some organizations and individuals to help refugees, the United States government largely resisted calls to increase the number of refugees allowed into the country.
Overall, the United States' lack of action during the Holocaust was a significant failure. The inability of the United States to provide assistance and protection to those who were being targeted by the Nazi regime contributed to the tragedy of the Holocaust and the loss of millions of lives.

The European Theater

The US and Britain achieved a complete wartime partnership. The cooperation between Roosevelt and Churchill ensured a common strategy. They decided from the outset that Germany posed a greater danger and thus gave priority to the European theater. 
From the outset, the US favored invasion across the English Channel. Army planners led by Chief of Staff George C. Marshall and his protégé, Dwight D. Eisenhower, were convinced that, that 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 navy attacks around the continent. As a result, they began by taking back Africa and then moving into Europe via Italy. 
General George Patton quickly rallied the troops and by May of 1943, Germany was driven from Africa.
The long awaited second front finally came on June 6, 1944. For two years, the US and England had focused on building up 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 Normandy peninsula, where an absence of good harbors led to lighter German fortifications. 
D-Day was originally set for June 5, but bad weather forced delay. On June 6, the invasion began.
  • The night before, three divisions parachuted down behind the German defenses.
  • At dawn, the British and American troops fought their way ashore.
  • By the end of the day, Eisenhower had won his beachhead. 
American tanks raced across the countryside and liberated Paris by the end of August. 
The end came quickly with a massive Russian offensive began and swept towards Berlin and the Americans and British came 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 would have flames reaching 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, pulling children out of their mothers' arms.
Twenty square miles of the city centre burned in an inferno that would rage for nine full days... The temperature in the firestorm reached 1,400 degrees Fahrenheit. There was no oxygen to breathe; whatever was flammable burst spontaneously into flame
By April, the armies had surrounded Berlin. Hitler refused to call for a retreat or surrender. He ordered all men, toddlers all the way to old 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” (basically retaking one island to the next, getting closer and closer to Japan) campaigns 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 and were ultimately besieged and surrendered in May 1942. When General Douglas MacArthur, the 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 to the main island with little food, water, or rest; coupled with rampant acts of violence, between 7,000 and 10,000 died on what was to be named the Bataan Death March.
Kamikaze (Japanese suicide planes) inflicted major damaged in the colossal Battle of Okinawa. Before finally succeeding in taking this island near Japan, US forces suffered 50,000 Success in the Pacific depended on control of the sea. 

Atomic Bomb

The defeat of Japan was now only a matter of time. The US had three possible ways to proceed. The decision would now be up to Harry S. Truman, as FDR died only a few short months into his unprecedented fourth term in office, just prior to the end of the war:
  • The military favored a full scale invasion. Causalities would have run into the hundreds of thousands. 
  • Diplomats suggested a negotiated peace, urging the US to modify the unconditional surrender formula to permit Japan to retain their emperor.
  • The third involved using the highly secret Manhattan Project
Since 1939, the US had spent $2 billion to develop and atomic bomb based on the fission of radioactive uranium and plutonium. Scientists, many of them refugees from Europe, worked to perfect this this deadly new weapon at the University of Chicago; Oak Ridge, TN; and Los Alamos, NM

Image Courtesy of Wikimedia

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 telltale mushroom cloud that rose some 40,000 feet. The desert sand turned to glass. 
Truman decided to utilize this new atomic bomb as viewed it as a way to save the lives of hundreds of thousands of Americans.
Weather on the morning of August 6 dictated the choice of Hiroshima as the bombs target. Other sites were considered, but virtually the rest of Japan had been destroyed by American bombing campaigns. Hiroshima was an industrial city. The explosion incinerated 4 square miles and instantly killed 60,000 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, that was the last atomic bomb the US had.
Three weeks later on the desk of 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.


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


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


The Big Three met again in February 1945 at the Yalta Conference. There agreement at Yalta would prove the most historic of the three meetings. After victory in Europe was achieved, 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 this 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.


In late July, after Germany’s surrender, only Stalin remained as one of the Big Three. Truman was the US president and Clement Attlee had just been elected the new British prime minister. The three leaders met in Potsdam and agreed:
  • To demand Japan surrender unconditionally
  • To hold war-crime trials of Nazi leaders
🎥 Watch: AP US History - World War II
Browse Study Guides By Unit
🌽Unit 1 – Interactions North America, 1491-1607
🦃Unit 2 – Colonial Society, 1607-1754
🔫Unit 3 – Conflict & American Independence, 1754-1800
🐎Unit 4 – American Expansion, 1800-1848
💣Unit 5 – Civil War & Reconstruction, 1848-1877
🚂Unit 6 – Industrialization & the Gilded Age, 1865-1898
🌎Unit 7 – Conflict in the Early 20th Century, 1890-1945
🥶Unit 8 – The Postwar Period & Cold War, 1945-1980
📲Unit 9 – Entering Into the 21st Century, 1980-Present
🚀Thematic Guides
🧐Multiple Choice Questions (MCQ)
📋Short Answer Questions (SAQ)
📝Long Essay Questions (LEQ)
📑Document Based Questions (DBQ)
📆Big Reviews: Finals & Exam Prep
✍️Exam Skills (MC, SAQ, LEQ, DBQ)

Stay Connected

© 2023 Fiveable Inc. All rights reserved.

© 2023 Fiveable Inc. All rights reserved.