AP World History Period 4 (1900–present) covers roughly 25% of the exam. It includes the World Wars, the Cold War, decolonization, and globalization — themes that appear frequently in DBQ prompts focusing on continuity and change in political systems and global connections.
World War I (1914–18)
MAIN causes — Militarism (arms race), Alliance system (Triple Entente vs. Triple Alliance), Imperialism (competition for colonies), Nationalism (especially in Balkans). Assassination of Franz Ferdinand triggered alliance cascade. Total war — mobilization of entire economies and populations; government rationing, women in factories, propaganda. New technologies — machine guns, poison gas, tanks, airplanes, submarines → trench warfare → stalemate on Western Front. Consequences — 20+ million dead; collapse of Ottoman, Austro-Hungarian, Russian, and German empires; Treaty of Versailles (war guilt, reparations, territorial losses) → economic and political instability → conditions for WWII.
Interwar Period and WWII
Russian Revolution (1917) — February Revolution (end of Tsar Nicholas II), October Revolution (Bolsheviks/Lenin seize power); civil war; USSR established; Comintern spread communist revolution globally. Great Depression — global economic collapse after 1929; mass unemployment; weakened democracies; fuel for fascism. Fascism — Mussolini in Italy (1922), Hitler in Germany (1933); extreme nationalism + authoritarian state + racial ideology + rejection of both capitalism and communism. Holocaust — Nazi genocide of 6 million Jews + millions of Roma, Slavs, disabled, LGBTQ+; systematic state-organized mass murder; Nuremberg Trials established concept of crimes against humanity. WWII consequences — 70+ million dead; US and USSR emerged as superpowers; decolonization accelerated; UN established; Marshall Plan reconstructed Western Europe.
Cold War
Bipolar world — US-led NATO vs. Soviet-led Warsaw Pact; nuclear deterrence (MAD — Mutually Assured Destruction). Proxy wars — US and USSR fought through allied states: Korea (1950–53), Vietnam (1955–75), Angola, Afghanistan (1979–89). Decolonization — rapid post-WWII independence: India (1947), Ghana (1957), Congo (1960), Algeria (1962); Cold War superpowers courted new nations; Non-Aligned Movement (Bandung Conference 1955). End of Cold War — Gorbachev's glasnost/perestroika; economic strain; Berlin Wall fell (1989); Soviet Union dissolved (1991).
Globalization (1990s–present)
Economic globalization — WTO, NAFTA, outsourcing of manufacturing to low-wage countries; multinational corporations; rising inequality within nations but decreasing poverty globally. Technology — internet, mobile phones, social media connected world; accelerated information flow; also enabled surveillance and disinformation. Migration — largest human migration in history; labor migration from South to North; refugee crises (Syria, Central America); xenophobia and nationalism backlash. Climate change — industrial carbon emissions → global warming; Paris Agreement (2016); disproportionate impact on Global South.
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