Q106: Why did the United States enter World War II?

A. The Japanese bombed Pearl Harbor
B. To support the Allied Powers (England, France, and eventually the Soviet Union)
C. To oppose the Axis Powers (Germany, Japan, and Italy)
D. All of the above

Question Background Information


Although World War I had done far less harm to America than to the European countries in whose territory it was largely fought, Americans nonetheless had little appetite for war in its aftermath. They had seen soldiers die and the costs of mobilization, such as the violation of civil liberties and the massive expansion of federal power necessary to make war. As such, Warren Harding had campaigned on a “return to normalcy,” and the traditional American invocation of George Washington’s Farewell Address, calling for the United States to minimize its participation in international political intrigue, resumed.

Expansionist dreams, and in the case of Germany and Italy, discontent with the Treaty of Versailles led the Axis Powers of Germany, Japan, and Italy to militarily invade nearby nations. As with the first world war, the United States initially avoided military intervention, but provided indirect aid—cutting off Japanese supplies while pressuring them to withdraw from the Chinese territory they had invaded, while, in the European theater, leasing military equipment to Britain and its allies. 

But the Japanese government, seeking to secure its resource base before American sanctions crippled it, making a possible future conflict with the Allies unwinnable, launched a sneak attack on the naval base at Pearl Harbor on December 7, 1941, in hopes of crippling the American navy. The United States declared war on Japan in response; Germany and Italy then fulfilled their treaty obligations by also declaring war on the United States. The United States soon joined the cause of the Allies: Great Britain (and its empire), the free French forces, China, and, following its betrayal by its previous German allies, the Soviet Union. 

Additional Content



Even though World War II ended in 1945, knowing who was involved and why is still important.  Just as the Treaty of Versailles influenced later events, World War II resulted in new national policies that continue to shape the world today.  This activity asks the students to look at the causes of the war and the goals of those who started it.  


  • Provide each group with a copy of the reading, the Cause of World War II.    
  • Provide each group with the Invasions of the Axis Powers handout
  • Provide each group with a grayscale printed copy of these three maps
  • Print a copy of the answer key to the Axis Powers handout for yourself

Required Files 

The Teaching Materials for this exercise includes an answer key.

Teaching Materials.


  • Have the students work in pairs. Divide the class into pairs based on the students’ individual levels. Group A is the group that needs some extra support. Group B is the core group that has the core knowledge to complete the activity. Group C is the enrichment group that has mastered the material. Group C students are prepared to extend their knowledge. Pair those who need support (Group A) with those who have core knowledge and/or have mastered the material (Groups B and C). 
    • This works equally well as an individual assignment. 
  • Provide the students with the necessary materials. 
    • Explain that they are going to create a map that details the causes of World War II and notes the aims of each Axis power.  
  • Circulate throughout the room as the students work on their maps. 
  • After the students complete their maps, lead a class discussion on the war using some or all of the prompts below: 
    • Name one new fact that you learned today about WWII.  
    • This activity focuses on the Axis rather than the Allies.  Why is it important to know why the Axis powers acted as they did?  How does this help our understanding of history?  
    • What role do you think the Great Depression had in the start of the war? 
    • Do you think that the war would have started if there was not a depression?  Why or why not? 
  • One of Mussolini’s goals was to unite the Italian people behind a common cause.  Why do you think this was important?  How would this help him in the long run?  (Hint: look at Japan) 
    • Why do you think the League of Nations failed to prevent WWII?  

Discussion Prompt


World War II stemmed from a number of issues and events, developing into a multi-front war that involved many nations throughout the world. 

Prompt 1 

World War II began in Europe in 1939, but the United States did not get involved until after the attack on Pearl Harbor on December 7, 1941.  Who did the United States fight in World War II?  What was the collective name of this “side” in the war?  Who were the Allied forces?  

Prompt 2 

The United States did not get involved in World War II until the Japanese bombed Pearl Harbor on December 7, 1941.  Prior to this, the U.S. attempted to remain neutral.  Why do you think that neutrality did not work in the long run?  What are the benefits to a nation remaining neutral?  What are the drawbacks?  Use current and past events to support your answer.