World War I and World War II
Two enormous global conflicts in the first half of the 1900s reshaped the world and made the United States a leading power. Knowing the basic causes, the U.S. role, and the outcomes of World War I and World War II covers a solid block of test questions.
World War I (1914–1918) and World War II (1939–1945) were the two largest wars in history. The U.S. entered each one later than the other major powers, and in both cases its involvement helped decide the outcome.
World War I
World War I grew out of rivalries among European powers, tangled alliances, militarism, and nationalism; the assassination of an Austrian archduke was the spark. The United States stayed neutral at first but entered in 1917, partly because of German submarine attacks on ships. American troops and resources helped the Allies win. The war ended in 1918, and the harsh Treaty of Versailles punished Germany — sowing resentment that would help cause the next war.
World War II
World War II began when Nazi Germany, led by Adolf Hitler, invaded its neighbors, while Japan expanded in Asia. The U.S. again stayed out until the Japanese attack on Pearl Harbor in December 1941 brought it into the war. The U.S. and its Allies fought the Axis powers (Germany, Italy, and Japan) on multiple fronts. The war in Europe ended in May 1945; the war with Japan ended after the U.S. dropped atomic bombs on Hiroshima and Nagasaki in August 1945. The Holocaust — the Nazi genocide of six million Jews — was one of history’s greatest atrocities.
Effects on the United States
Both wars transformed America. They pulled the economy out of downturns, expanded the role of government, and drew millions of women and minorities into the workforce. After World War II, the U.S. emerged as a global superpower, and its rivalry with the Soviet Union led straight into the Cold War. The wars also led to new international bodies — the League of Nations after WWI and the United Nations after WWII — meant to prevent future conflicts.
Watch: A Short Video Lesson
CrashCourse gives a clear overview to go with this lesson:
A Routine for World War Questions
- WWI: alliances and nationalism; U.S. entered in 1917; Treaty of Versailles punished Germany.
- WWII: Axis aggression; U.S. entered after Pearl Harbor (1941); ended 1945.
- The Holocaust was the Nazi genocide of six million Jews.
- After WWII the U.S. became a superpower and the UN was formed.
Practice
- Name one underlying cause of World War I.
- What event brought the U.S. into World War II?
- Which treaty ended World War I and punished Germany?
- Who were the Axis powers in World War II?
- What was the Holocaust?
- What international organization was formed after World War II?
Answers
- Any of: alliances, militarism, nationalism, imperial rivalry.
- The Japanese attack on Pearl Harbor.
- The Treaty of Versailles.
- Germany, Italy, and Japan.
- The Nazi genocide of six million Jews.
- The United Nations.
Where This Fits in Your Social Studies Prep
The world wars lead into the Cold War and U.S. foreign policy, and they connect to the economic crises of the era. See every topic on the Social Studies Prep Hub.
Recommended Prep Books
These study guides and practice books help you keep building momentum as you prepare:
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