Major Events of the World Wars

Why This Matters

When you encounter questions about major wars in world history, you're not just being tested on dates and death tolls—you're being asked to understand how conflicts reshape political systems, redraw borders, and shift global power. These wars demonstrate recurring patterns: the role of alliance systems in escalating local disputes into global catastrophes, the way technological innovation transforms warfare, and how peace settlements often plant the seeds for future conflicts. From the Peace of Westphalia establishing modern state sovereignty to the Treaty of Versailles creating conditions for World War II, each war's aftermath matters as much as its battles.

As you study these conflicts, focus on the causes, turning points, and consequences that connect them across centuries. Notice how religious wars gave way to nationalist wars, how colonial rivalries fueled global conflicts, and how ideological struggles defined the twentieth century. Don't just memorize which countries fought whom—know what principle each war illustrates and how its outcome changed the international order. That's what earns you points on FRQs.

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Wars That Established the Modern State System

These early modern conflicts transformed Europe from a patchwork of feudal and religious loyalties into a system of sovereign nation-states—the foundation of international relations you'll study throughout the course.

Thirty Years' War (1618-1648)

• Began as a religious conflict between Catholics and Protestants in the Holy Roman Empire—the last major European war fought primarily over religion
• Evolved into a political power struggle involving France, Sweden, Spain, and the Habsburgs, devastating Central Europe and killing roughly one-third of the German population
• Ended with the Peace of Westphalia, establishing state sovereignty and the principle of cuius regio, eius religio (the ruler determines the religion), marking the birth of the modern international system

Napoleonic Wars (1803-1815)

• Spread revolutionary ideals across Europe as Napoleon's conquests dismantled old monarchies and introduced the Napoleonic Code—a standardized legal system emphasizing equality before the law
• Featured decisive battles including Austerlitz (1805), Napoleon's tactical masterpiece, and Waterloo (1815), his final defeat by British and Prussian forces
• Concluded with the Congress of Vienna, which restored monarchies and established a balance of power system designed to prevent any single nation from dominating Europe

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Imperial Rivalries and Global Expansion

These conflicts demonstrate how competition for colonies, resources, and prestige among European powers—and rising non-European powers—created flashpoints that exploded into war.

Seven Years' War (1756-1763)

• Often called the first "world war" because fighting occurred simultaneously in Europe, North America (French and Indian War), the Caribbean, and India
• Resulted in Britain's emergence as the dominant colonial power, gaining French Canada and Spanish Florida while France lost most of its North American territory
• Created colonial tensions through British taxation to pay war debts—directly contributing to the American Revolution just thirteen years later

Crimean War (1853-1856)

• Exposed Ottoman weakness as Russia sought to expand into Ottoman territory, prompting Britain and France to intervene and check Russian ambitions in the Mediterranean
• Introduced modern warfare elements including the telegraph, war photography, and Florence Nightingale's nursing reforms—the first war covered extensively by journalists
• Demonstrated the breakdown of the Concert of Europe, the cooperative system established at Vienna, as great powers openly fought each other for the first time since 1815

Russo-Japanese War (1904-1905)

• First modern victory of an Asian power over a European power, shattering assumptions of Western military superiority and inspiring anti-colonial movements worldwide
• Fought over imperial control of Manchuria and Korea, with Japan's surprise attack on the Russian fleet at Port Arthur setting the tone
• Ended with the Treaty of Portsmouth (mediated by U.S. President Theodore Roosevelt), recognizing Japan as a major imperial power and humiliating Russia—contributing to the 1905 Russian Revolution

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The World Wars: Total War and Global Transformation

These twentieth-century conflicts introduced total war—the mobilization of entire societies, economies, and technologies for military purposes—and fundamentally restructured the international order.

World War I (1914-1918)

• Triggered by the assassination of Archduke Franz Ferdinand, but caused by deeper factors: alliance systems (Triple Entente vs. Triple Alliance), imperial rivalries, militarism, and nationalism—remember the acronym MAIN
• Introduced industrialized slaughter through trench warfare, machine guns, poison gas, and artillery, creating a bloody stalemate on the Western Front with millions of casualties
• Ended with the Treaty of Versailles, which imposed war guilt and crushing reparations on Germany, redrew European borders creating new nations, and—critically—planted seeds of resentment that fueled World War II

World War II (1939-1945)

• Initiated by Nazi Germany's invasion of Poland on September 1, 1939, following years of appeasement that failed to stop Hitler's territorial expansion
• Featured unprecedented horrors and turning points: the Holocaust (systematic murder of six million Jews), the Battle of Stalingrad (turning point on the Eastern Front), D-Day (Allied invasion of Normandy), and the atomic bombings of Hiroshima and Nagasaki
• Created the modern world order through the United Nations, the Cold War division between U.S. and Soviet spheres, decolonization movements, and the beginning of the nuclear age

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Ideological Conflicts of the Modern Era

These wars were fought not just over territory but over competing visions of how societies should be organized—capitalism vs. communism, democracy vs. authoritarianism.

American Civil War (1861-1865)

• Fought over slavery and states' rights, with the Confederacy seceding to preserve the institution of slavery and the Union fighting to preserve the nation—Lincoln's Emancipation Proclamation (1863) transformed it into a war for freedom
• Demonstrated industrial warfare's devastation through battles like Gettysburg (turning point, highest casualties) and Antietam (bloodiest single day), with over 600,000 total deaths
• Resulted in the Thirteenth Amendment abolishing slavery and fundamentally altered federalism, strengthening national government power over states

Korean War (1950-1953)

• First major "hot war" of the Cold War, beginning when communist North Korea invaded South Korea, prompting a UN military response led by the United States
• Demonstrated Cold War dynamics as China intervened to support North Korea, creating a bloody stalemate around the 38th parallel—the same dividing line that exists today
• Ended with an armistice, not a peace treaty, leaving Korea divided and technically still at war—a frozen conflict that remains a flashpoint in international relations

Vietnam War (1955-1975)

• Rooted in anti-colonial struggle as Ho Chi Minh's communist forces fought first France, then the U.S.-backed South Vietnamese government—demonstrating the limits of superpower intervention
• Characterized by guerrilla warfare and the Tet Offensive (1968), which turned American public opinion against the war despite being a military defeat for North Vietnam
• Ended with the fall of Saigon (1975) and communist reunification of Vietnam, marking a major Cold War defeat for the U.S. and inspiring anti-war movements worldwide

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Quick Reference Table

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Self-Check Questions

1. Which two wars both resulted in peace settlements that attempted to create a new international order based on balance of power? What was similar and different about the Congress of Vienna and the Treaty of Versailles?

2. Identify two conflicts that demonstrated the decline or limitation of European/Western power. What did each reveal about changing global dynamics?

3. Compare the causes of World War I and World War II. How did the settlement of WWI contribute to the outbreak of WWII?

4. Which wars on this list could be classified as "ideological conflicts"? What ideologies were in competition in each case?

5. If an FRQ asked you to trace the development of the modern state system from 1648 to 1945, which three wars would you use as key turning points, and why?