World War II (1939–1945): Origins, Fighting a Global War, and Human Consequences

Treaty of Versailles (1919)

Post–World War I treaty that imposed territorial losses, military restrictions, and reparations on Germany, creating grievances and resentment many later exploited.

Legitimacy (of a peace settlement)

The extent to which a postwar agreement is seen as “fair enough” to endure; low legitimacy can fuel resentment and political radicalization.

Self-determination

The principle that ethnic/national groups should have their own states; after WWI it clashed with imperial realities and imperfect borders.

Minority tensions (interwar Europe)

Conflicts created when new/reconfigured states still contained significant ethnic minorities, leading to disputes over territory and identity.

League of Nations

International organization created after WWI to prevent war through diplomacy; struggled due to weak enforcement and inconsistent great-power commitment.

Collective security

Idea that aggression against one state should be met by a unified response from many states; depends on major powers’ willingness and ability to enforce it.

Great Depression (beginning 1929)

Global economic crisis that intensified unemployment and hardship, weakening moderate governments and strengthening extremist and authoritarian movements.

Political extremism (interwar period)

Growth of radical parties and movements during economic and political instability, often offering simple blame narratives and favoring authoritarian solutions.

Revisionist powers

States (notably Germany, Italy, Japan) that sought to revise post–WWI borders, treaties, or imperial influence, destabilizing the international order.

Status quo powers

States that generally wanted to preserve the post–WWI settlement or at least avoid another major war.

Fascism

Authoritarian ideology emphasizing intense nationalism, a powerful state under a charismatic leader, unity, and acceptance of violence to achieve national greatness.

Nazism

German authoritarian ideology combining extreme racial beliefs with intense nationalism and the goal of overturning the Treaty of Versailles through expansion.

Japanese militarism (interwar)

Rising influence of military leaders in Japan who promoted imperial expansion in Asia as a solution to strategic and resource concerns.

Lebensraum

Nazi concept of “living space,” used to justify German territorial expansion as necessary for the nation’s future and linked to racial ideology.

Greater East Asia Co-Prosperity Sphere

Japanese justification for expanding in Asia as “Asia for Asians,” which in practice often meant Japanese dominance over occupied territories.

Appeasement

Policy of making concessions to aggressor states to avoid war; in the 1930s it often signaled weak resolve and encouraged further aggression.

Munich Agreement (1938)

Agreement allowing Germany to annex the Sudetenland from Czechoslovakia, illustrating how concessions could be extracted through pressure.

Nazi-Soviet Pact (1939)

Non-aggression agreement between Germany and the Soviet Union that reduced Germany’s short-term fear of a two-front war and enabled the invasion of Poland.

Invasion of Poland (1939)

German attack that is commonly dated as the start of WWII in Europe; triggered wider war due to British and French alliance commitments.

Total war

Warfare in which states mobilize entire societies—economies, labor, science, and civilian morale—blurring the line between front lines and home front.

Blitzkrieg

“Lightning war” tactic using fast combined arms (air power, tanks, motorized infantry) to break lines, encircle forces, and win rapid victories.

Operation Barbarossa (1941)

Germany’s invasion of the Soviet Union, opening a massive Eastern Front and contributing to a draining war of attrition.

Island hopping

Pacific strategy of capturing key islands to move closer to Japan while bypassing some heavily fortified positions, shifting momentum through naval/air power.

Holocaust

Nazi Germany’s systematic, state-driven genocide of Europe’s Jews (and persecution/murder of other targeted groups), enabled by ideology, bureaucracy, and wartime conditions.

Nanjing Massacre (1937–1938)

Mass killings and sexual violence committed by Japanese troops after capturing Nanjing, exemplifying atrocities linked to imperial warfare and dehumanization in Asia.