AP World History Unit 7 Essentials: Key Terms & Big Ideas

Big Idea 1

WWI was caused by the collision of nationalism, militarism, imperialism, and alliance systems

The assassination of Archduke Franz Ferdinand was a trigger, not a cause. The underlying causes — intense nationalism among European powers, a rigid alliance system, imperial competition, and massive military buildups — created a powder keg. Understanding MAIN (Militarism, Alliances, Imperialism, Nationalism) is essential for any AP World exam question on WWI's origins.

WWI CausesMAINNationalism

Big Idea 2

The Treaty of Versailles planted the seeds of WWII

The punitive peace imposed on Germany after WWI — massive reparations, war guilt, territorial losses — created economic devastation and national humiliation that Hitler exploited. The Great Depression made conditions worse. WWII is unintelligible without understanding how the "peace" of 1919 failed to create lasting stability.

VersaillesInterwar PeriodCausation

Big Idea 3

WWII was the deadliest conflict in human history — and reshaped the world order

An estimated 70–85 million people died in WWII — the majority civilians. The war ended European dominance of global affairs, established the US and USSR as superpowers, created the United Nations, and set the stage for decolonization. The use of atomic bombs on Hiroshima and Nagasaki inaugurated the nuclear age and changed the nature of warfare forever.

WWIIAtomic BombWorld Order

Big Idea 4

Genocide became a defining horror of the 20th century

The Holocaust was not an isolated atrocity — it was part of a century marked by state-organized mass killings. The Armenian Genocide (WWI), the Holocaust (WWII), and later genocides in Cambodia, Rwanda, and Bosnia all share common features: dehumanizing propaganda, state power, and international failure to intervene. The 20th century forced the world to grapple with the concept of "crimes against humanity."

GenocideHolocaustHuman Rights

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Total War

A war requiring complete mobilization of a nation's military, industrial, and civilian resources; WWI and WWII blurred the distinction between soldiers and civilians.

Warfare

Trench Warfare

WWI military strategy of dug-in defensive positions along the Western Front; produced horrific casualties with little territorial gain and symbolized the industrial nature of modern warfare.

WWI

Treaty of Versailles (1919)

Peace treaty ending WWI; imposed massive reparations and war guilt on Germany, stripped it of territory, and created conditions that fueled the rise of fascism and WWII.

WWI Aftermath

Fascism

Authoritarian ultranationalist ideology emphasizing dictatorial power, state control, and violent suppression of opposition; rose in Italy (Mussolini) and Germany (Hitler) during the economic devastation of the 1930s.

Political Ideology

Holocaust

The systematic, state-sponsored genocide of six million Jews and millions of others (Roma, disabled people, political dissidents) by Nazi Germany between 1941 and 1945.

Genocide

Armenian Genocide

Systematic mass killing and deportation of 1–1.5 million Armenians by the Ottoman government during WWI (1915–1916); one of the first genocides of the 20th century.

Genocide

League of Nations

International organization created after WWI to maintain peace through collective security; fatally weakened by U.S. non-membership and failure to prevent WWII aggression.

International Organizations

Great Depression

Global economic collapse beginning with the 1929 U.S. stock market crash; caused massive unemployment worldwide and created political conditions favorable to extremist movements.

Economics

Propaganda

Information — often biased or misleading — used by governments to manipulate public opinion; WWI and WWII saw industrialized propaganda campaigns that shaped how entire populations understood the war.

Media & Power

MAIN Causes of WWI

Acronym for the four underlying causes of WWI: Militarism (arms buildup), Alliances (Triple Entente vs Triple Alliance), Imperialism (colonial competition), Nationalism (especially in the Balkans).

WWI Causes

Russian Revolution (1917)

Two revolutions that overthrew the Russian tsar and brought the Bolsheviks (led by Lenin) to power; established the world's first communist state, the Soviet Union.

Revolution

Vladimir Lenin

Bolshevik leader of the Russian Revolution; founded the Soviet Union and adapted Marxism for a peasant-majority Russia; "Lenin's revisions" of Marxism became known as Marxism-Leninism.

Russia

Adolf Hitler

Leader of Nazi Germany (1933–1945); rose to power exploiting Treaty of Versailles resentment and Great Depression conditions; led WWII in Europe and orchestrated the Holocaust.

WWII

Benito Mussolini

Italian fascist dictator (1922–1943); originator of fascism as a political movement and Hitler's primary ally; executed by Italian partisans in 1945.

Fascism

Joseph Stalin

Soviet dictator (1924–1953); led the USSR through forced industrialization (Five-Year Plans), the Great Purges, victory in WWII, and the start of the Cold War.

Soviet Union

Blitzkrieg

"Lightning war" — German tactic of fast, coordinated attacks combining tanks, infantry, and air power; enabled rapid Nazi conquest of Poland, France, and the Low Countries.

WWII Tactics

Pearl Harbor

Japanese surprise attack on the US Pacific Fleet (December 7, 1941); brought the United States into WWII as a combatant.

WWII

D-Day

Allied invasion of Nazi-occupied France on June 6, 1944; the largest seaborne invasion in history; opened the Western front and began the liberation of Western Europe.

WWII

Atomic Bomb

Nuclear weapons developed by the US in the Manhattan Project and used on Hiroshima (Aug 6, 1945) and Nagasaki (Aug 9, 1945); ended WWII and inaugurated the nuclear age.

Nuclear Age

United Nations

International organization founded in 1945 to replace the failed League of Nations; maintains the modern framework for diplomacy, peacekeeping, and human rights.

International Organizations