The crisis of European hegemony.

By 1900, several pressures had built up. Germany (united 1871) was an industrial powerhouse with a small colonial empire and wanted “a place in the sun.” Britain felt threatened. Russia, weakened by the 1905 revolution, sought stability through alliance. Austria-Hungary was a multinational empire fragmenting under nationalist pressure (especially in the Balkans). The Ottoman Empire was visibly declining. Alliance systems (Triple Alliance vs. Triple Entente) hardened these tensions into commitments that would convert any local conflict into a continental one.

Long-term causes (MAIN): Militarism (arms race, especially German naval expansion), Alliances (Triple A vs. Triple E), Imperialism (colonial competition), Nationalism (especially in the Balkans). Short-term cause: The June 28, 1914 assassination of Archduke Franz Ferdinand by Gavrilo Princip in Sarajevo. Austria-Hungary issued an ultimatum to Serbia; Russia mobilized; Germany declared war on Russia and France; Britain declared war on Germany after the German invasion of Belgium. Within five weeks, all of Europe was at war.

On the Western Front, machine guns and barbed wire made offense suicidal; battles like Verdun and the Somme each killed hundreds of thousands. Total war mobilized civilian economies: rationing, women in factories, propaganda. Theaters extended beyond Europe: the Ottomans fought British and Arab forces in the Middle East; Africa’s colonies were drawn in; Japan seized German Pacific holdings. New technology: poison gas, tanks, aircraft, submarines. The war that everyone expected to be “over by Christmas” lasted four years.

The 1920s seemed prosperous in the U.S. and (briefly) Germany, but the gold-standard global economy was fragile. The 1929 U.S. stock market crash exposed and amplified weaknesses: bank failures, deflation, demand collapse. By 1933, U.S. unemployment hit 25%; German unemployment was higher. Governments responded variously: U.S. New Deal (federal jobs and welfare), German Nazi remilitarization, Soviet Five-Year Plans, Japan’s aggressive imperial expansion. The Depression discredited liberal capitalism in much of the world and empowered radical alternatives.

The Treaty of Versailles (1919) imposed war guilt and ~$33 billion in reparations on Germany, redrew European borders, and dismantled the Ottoman Empire into League of Nations Mandates run by the victors. Wilson’s League of Nations was created but the U.S. didn’t join. Italy felt cheated of promised territory. Japan saw racial inequality clauses rejected. Germans saw the treaty as a national humiliation. The interwar order was built on resentments that fascist movements would exploit. By 1939, Hitler had unwound it.

Causes: Hitler’s revanchist Germany rearmed (1935), reoccupied the Rhineland (1936), absorbed Austria (Anschluss 1938), and annexed the Sudetenland after the Munich Agreement (1938). Britain and France’s appeasement encouraged him; the Molotov-Ribbentrop Pact (Aug 1939) cleared his eastern flank. Italy invaded Ethiopia (1935). Japan invaded Manchuria (1931) and China (1937), then Pearl Harbor (Dec 1941). The war that began September 1939 became truly global by late 1941.

The Eastern Front was the bloodiest: Operation Barbarossa (June 1941) cost millions of Soviet lives but bled the Wehrmacht; Stalingrad (1942–43) and Kursk (1943) were turning points. The Western theater: Battle of Britain (1940), Italian and North African campaigns, D-Day (June 1944), Battle of the Bulge, V-E Day (May 1945). The Pacific: Pearl Harbor, Midway (1942), island-hopping, the firebombing of Japanese cities, atomic bombs (Hiroshima Aug 6, Nagasaki Aug 9, 1945). Total war meant civilian targeting was the norm, not the exception.

The 20th century industrialized atrocity. The Armenian genocide (1915–1923) killed ~1.5 million. The Holocaust (1941–1945) killed 6 million Jews and ~5 million others (Roma, disabled, Soviet POWs, gay men). Stalin’s Holodomor (1932–33) killed millions of Ukrainians. The Rape of Nanjing (1937), the Bengal famine (1943), the firebombing of Dresden and Tokyo, the atomic bombings—each tested what “war” and “civilian” could mean. The 1948 Genocide Convention and Universal Declaration of Human Rights tried to set new limits.

Strong causation analysis: WWI causes (long-term + short-term + structural). WWII causes (Versailles + Depression + ideology + appeasement). Both wars: industrialization made total war possible; nationalism made it desirable to leaders; alliance systems made local conflicts global. WWI directly caused WWII via Versailles, Soviet Union, fascism, and unresolved ethnic tensions. The chain is exactly the kind of multi-step causation the exam loves to test.