World War I and the Remaking of Europe (1914–1919)

Causes of World War I

World War I (1914–1918) did not begin because Europeans suddenly became irrational in the summer of 1914. It began because several long-term pressures had built a system that was powerful but brittle—like a machine with many gears moving at once. When the “spark” arrived, leaders made choices inside that system that turned a regional crisis into a general European war.

A strong way to learn causation in AP Euro is to separate long-term causes (conditions that made a major war more likely) from short-term causes (decisions and events that triggered the war when they did). You’ll also want to practice explaining how one cause led to another rather than listing factors.

The “MAIN” long-term causes (and how they worked)

You’ll often see the acronym MAIN—Militarism, Alliances, Imperialism, Nationalism—because it helps you remember the major categories. The key is to understand the mechanism for each.

Nationalism

Nationalism is the belief that people who share a language, culture, or history should have political unity and loyalty—often expressed through a nation-state. In early 20th-century Europe, nationalism mattered because it both unified and destabilized empires.

How it pushed Europe toward war: Nationalism created intense rivalries (France vs. Germany, Slavs vs. Habsburg authorities) and made compromise politically risky. Leaders feared looking “weak” in public, especially in crises.

Where it was most explosive: The Balkans, where the weakening Ottoman Empire left a power vacuum and many ethnic groups sought independence or expansion. Serbian nationalism and the idea of uniting South Slavs (“Yugoslav” nationalism) threatened Austria-Hungary, a multiethnic empire.

Common misconception to avoid: Nationalism did not automatically cause war everywhere. It became dangerous when paired with great-power competition and fragile empires.

Imperialism

Imperialism is the policy of extending a nation’s power by acquiring colonies or spheres of influence. By 1900, European states competed for overseas territory, markets, and prestige.

How it pushed Europe toward war: Imperialism intensified distrust—especially in crises like Morocco (where Germany challenged French influence). Even when colonial disputes were settled without war, they deepened the sense that international politics was a zero-sum competition.

Important nuance: Colonial rivalry wasn’t the direct trigger in 1914, but it helped poison diplomacy and encouraged military planning.

Militarism

Militarism is the glorification of the military and the belief that armed force is a normal and effective tool of national policy. In pre-1914 Europe, militarism showed up in:

• Large standing armies and conscription
• Arms races (including naval competition)
• War planning that assumed rapid mobilization

How it pushed Europe toward war: Mobilization plans became “use them or lose them.” Because rail timetables and troop movements were complex, leaders treated mobilization as nearly irreversible. That made diplomacy harder during the July 1914 crisis—once one state mobilized, others felt compelled to respond.

Example in action: Germany’s Schlieffen Plan (a strategic plan to avoid fighting France and Russia simultaneously by quickly defeating France first) encouraged speed and risk-taking. If leaders believed war was likely, they could see advantages in striking first.

Alliances

An alliance system is a set of diplomatic and military agreements linking states together. Before WWI, alliances were meant to deter aggression by promising support. But they also created a situation where a conflict between two countries could pull in many others.

Key alignments:

How it pushed Europe toward war: Alliances created commitments and expectations. In a crisis, leaders feared that failing to support an ally would permanently weaken their position.

Important nuance (often tested): Alliances did not make war “automatic.” States still made choices. For example, Italy—originally in the Triple Alliance—did not join the war on Germany’s side in 1914 and later entered on the Allied side in 1915.

The Balkan powder keg and the July Crisis (short-term causes)

Short-term causation is about timing: why war broke out in 1914 and not earlier.

The Balkans before 1914

The Balkans were unstable due to:

• The decline of Ottoman power in southeastern Europe
• Competing ambitions of Austria-Hungary and Russia
• Local nationalist movements (especially Serbia)

Crises and wars in the region in the years before 1914 made leaders more suspicious and more willing to consider force.

The assassination and the chain reaction

On June 28, 1914, Archduke Franz Ferdinand, heir to the Austro-Hungarian throne, was assassinated in Sarajevo by Gavrilo Princip, a Bosnian Serb nationalist associated with a wider Serbian nationalist network.

The assassination mattered less as a “cause” by itself and more as an opportunity: Austria-Hungary chose to confront Serbia forcefully, believing its empire’s survival was at stake.

A simplified step-by-step of the July Crisis:

1. Austria-Hungary decides to punish Serbia and issues a harsh ultimatum.
2. Germany offers strong diplomatic backing to Austria-Hungary (often called the “blank check”), which encourages Austria-Hungary to act aggressively.
3. Russia, seeing itself as protector of Slavic peoples and fearing loss of influence, moves toward supporting Serbia.
4. Mobilizations and counter-mobilizations accelerate.
5. Germany declares war on Russia and France; Germany’s invasion of Belgium helps bring Britain into the war.

Why this sequence matters: AP exam questions often reward you for showing how decisions under pressure interacted with structural factors like alliances and mobilization.

Worked example: turning a list into a causal explanation

Instead of writing: “WWI was caused by nationalism, imperialism, alliances, and militarism,” you want an explanation like:

Because European states relied on rigid mobilization plans and expected allied support, Austria-Hungary’s attempt to crush Serbia after the assassination quickly escalated. Russian partial mobilization, intended to deter Austria-Hungary, was interpreted by Germany as a threat that required immediate action under the Schlieffen Plan, widening a Balkan crisis into a continental war.

Notice what that does: it connects militarism (planning), alliances (commitments), and nationalism (Balkan tensions) through a clear mechanism.

Exam Focus

• Typical question patterns
  • Explain the relative importance of long-term causes (MAIN) versus the July Crisis in causing WWI.
  • Compare how nationalism operated differently in Western Europe (e.g., France/Germany) versus Eastern/Southeastern Europe (multiethnic empires).
  • Use evidence from diplomacy or military planning (alliances, mobilization, Schlieffen Plan) to explain escalation.
• Common mistakes
  • Treating the assassination as the sole cause—without explaining why it escalated into a general war.
  • Claiming alliances made war inevitable; you need to show choices and contingency in 1914.
  • Writing only a list of factors with no “because/therefore” causal chain.

World War I: A Total War

World War I is often described as total war—a conflict in which states mobilize not just armies but entire societies and economies, blurring the line between front lines and home front. Understanding total war helps you explain changes in government power, social roles, and postwar instability.

What “total war” meant in practice

Total war wasn’t a slogan; it was a set of linked developments.

Mass mobilization and the power of the state

European governments expanded control over daily life because modern industrial war required predictable supplies of men, food, weapons, and morale.

• Conscription and massive armies meant millions of soldiers under arms.
• Governments coordinated production, transportation, and labor.
• Civil liberties were often restricted through censorship and emergency powers.

Why it matters: Once states learn to manage economies and public opinion at this scale, those tools don’t disappear after the war. This is one reason WWI is a turning point toward greater state intervention in the 20th century.

Industrialized killing and new military technology

WWI showcased how industrial capacity could be converted into battlefield power.

• Machine guns and heavy artillery favored defense.
• Trench warfare emerged, especially on the Western Front, because attacking across open ground against modern firepower was devastating.
• Poison gas was used (notably beginning in 1915 on a large scale), though it was not usually decisive by itself.
• Tanks were introduced during the war (notably in 1916), gradually improving the ability to cross trenches.
• Aircraft evolved from reconnaissance to combat roles.
• Submarine warfare (especially German U-boats) targeted shipping.

How it worked: When defensive technologies are stronger than offensive tactics, armies dig in. The result is attrition—trying to wear down the enemy’s manpower and morale. Battles like Verdun (1916) and the Somme (1916) are remembered because they symbolize this logic.

Common misconception: New weapons did not automatically produce quick victory. Early tanks and planes were limited; leadership and strategy lagged behind technology.

The home front: propaganda, rationing, and labor

Total war required that civilians accept sacrifice.

• Propaganda framed the war as a moral struggle, encouraging enlistment, work discipline, and hatred of the enemy.
• Rationing and price controls became common as states redirected food and raw materials.
• Women entered wartime industries and services in expanded numbers, not necessarily ending gender inequality but reshaping debates about citizenship and suffrage.

Analogy that helps: Think of the economy as a household budget. In peacetime, you choose spending based on preference; in total war, the government rewrites the budget, deciding what industries grow, what goods are scarce, and what people must do.

Global dimensions and “total” geopolitics

Although you often study trenches in France and Belgium, WWI was also global:

• Fighting occurred in and involved colonial territories.
• Naval blockades and worldwide supply chains mattered.
• The United States entered the war in April 1917, tipping the balance in resources and morale.

Worked example: how total war changes politics

If a government tells workers what to produce, tells farmers what to sell, limits newspapers, drafts men, and promotes propaganda, then “winning” becomes tied to internal control. That helps explain:

• Rising labor unrest when shortages worsen
• Political radicalization when casualties mount
• Postwar expectations that the state should provide jobs and security (or, alternatively, fears that the state has become too powerful)

What went wrong: stalemate, radicalization, and fragile morale

Total war created pressure-cooker conditions.

• Stalemate made victory seem distant, increasing despair.
• High casualties eroded faith in old elites.
• Civilian hardship encouraged strikes and protests.

These pressures are essential background for understanding revolutions and political extremism after 1917.

Exam Focus

• Typical question patterns
  • Explain how WWI was “total war” using specific evidence from the home front (rationing, propaganda, state control) and the front (technology, trenches).
  • Analyze how the experience of total war changed the relationship between citizens and the state.
  • Connect wartime hardships to political instability (including revolution and postwar extremism).
• Common mistakes
  • Describing only trench warfare and ignoring the home front (a frequent scoring limitation).
  • Assuming women’s wartime work produced immediate, uniform equality; effects varied by country and period.
  • Treating technology as the sole explanation for stalemate without discussing strategy, logistics, and defensive advantages.

The Russian Revolution

The Russian Revolution refers to the collapse of the tsarist system in 1917 and the eventual Bolshevik takeover that led to the world’s first communist state. In AP European History, this topic matters because it shows how total war can destroy regimes, and because it reshaped European politics by creating a powerful ideological alternative to liberal capitalism.

Why Russia was vulnerable before 1917

Russia entered World War I with deep structural weaknesses.

• The autocratic political system under Tsar Nicholas II limited peaceful reform.
• Rapid industrialization existed alongside vast rural poverty.
• Social tensions (workers, peasants, national minorities) had already produced unrest, including the 1905 Revolution.

This matters because WWI didn’t create Russian problems from scratch; it magnified them. When the state failed to manage war effectively, people blamed the regime itself.

How World War I triggered collapse

WWI strained Russia in several connected ways:

1. Military failures and enormous casualties discredited leadership.
2. Economic breakdown disrupted transport and food supply, especially to cities.
3. Political credibility collapsed as the tsar took greater personal responsibility for the war effort, making him a direct target for blame.

A useful way to think about this: in total war, the regime makes an implicit promise—“Endure hardship now and we will protect the nation.” When the state cannot deliver victory or basic survival, legitimacy evaporates.

The February/March Revolution and the Provisional Government

In February 1917 (March by the Western calendar), strikes and demonstrations in Petrograd escalated. Soldiers mutinied rather than suppress crowds, and Nicholas II abdicated.

A Provisional Government formed, aiming for a liberal constitutional order. But it faced a fatal dilemma:

• If it continued the war, it remained tied to suffering and shortages.
• If it exited the war, it risked humiliation and loss of Allied support.

At the same time, soviets (workers’ and soldiers’ councils) exerted grassroots authority, producing a situation often described as “dual power.”

Common misconception: The February/March Revolution did not immediately create a communist state. It created a crisis of authority in which multiple groups claimed legitimacy.

The Bolshevik Revolution (October/November 1917)

The Bolsheviks, led by Vladimir Lenin, argued that the Provisional Government could not solve Russia’s core problems—war, land, hunger—and that power should go to the soviets.

In October 1917 (November Western calendar), the Bolsheviks seized key points in Petrograd and overthrew the Provisional Government.

How it worked (mechanism over myth): The Bolshevik success depended on organization, clear slogans (“Peace, Land, Bread”), and the Provisional Government’s weakening authority. It was not simply a spontaneous uprising of the entire population.

Civil war and the consolidation of Bolshevik power

The Bolsheviks (Reds) faced opposition (Whites and others) in a civil war that lasted into the early 1920s. During this period:

• The regime centralized authority.
• Political violence expanded (including the Red Terror).
• The economy was placed under emergency controls often associated with War Communism.

A major turning point was Russia’s exit from WWI through the Treaty of Brest-Litovsk (March 1918), in which Russia accepted major territorial losses to Germany. This helped the Bolsheviks focus on the civil war but fueled opposition by making them seem willing to sacrifice national territory.

After the civil war, Lenin introduced the New Economic Policy (NEP) in 1921, allowing limited market mechanisms to revive production.

Why this matters for Europe: The revolution terrified many European elites and inspired leftist movements, contributing to polarization—fear of communism on one side, revolutionary hopes on the other.

Worked example: explaining “why the Bolsheviks won”

A strong causal explanation might argue:

• The Provisional Government lost support by continuing the war and failing to address land and food.
• The Bolsheviks offered simple, urgent solutions and built disciplined party organization.
• Control of key cities and institutions at critical moments mattered more than universal popularity.

This kind of explanation scores better than vague statements like “people wanted communism.”

Exam Focus

• Typical question patterns
  • Analyze how WWI conditions (military defeat, shortages, political delegitimization) contributed to revolution.
  • Compare the aims and legitimacy of the Provisional Government and the soviets/Bolsheviks.
  • Evaluate whether the Bolshevik Revolution was primarily ideological, political, or driven by wartime crisis.
• Common mistakes
  • Collapsing 1917 into one event; you must distinguish February/March from October/November.
  • Treating the Bolshevik takeover as inevitable; AP responses should show contingency and competing forces.
  • Ignoring the civil war and state-building phase, which explains how the regime survived.

Versailles Settlement and Its Effects

The Versailles Settlement refers to the peace agreements made after WWI, especially the Treaty of Versailles (June 28, 1919) with Germany. In AP European History, you study it not only as a set of terms but as a turning point that shaped interwar politics—creating new states, new resentments, and new international ambitions.

What the peacemakers were trying to do

The Allied leaders had overlapping but conflicting goals:

• Security: prevent another German attack, especially demanded by France.
• Self-determination: the idea that peoples should have their own states, associated with U.S. President Woodrow Wilson’s rhetoric.
• Balance of power and empire: Britain and France also considered colonial interests and strategic advantage.

These goals often clashed. For example, self-determination was easier to promise than to implement in regions with mixed ethnic populations.

Key elements of the Treaty of Versailles

When you learn the treaty, avoid memorizing a random list. Instead, organize it by what it attempted to change.

Territorial changes and new states

Germany lost territory and all its overseas colonies (reassigned as mandates under the League of Nations system). In Central and Eastern Europe, new or reconfigured states emerged as empires collapsed (notably the Austro-Hungarian and Russian empires), including a reconstituted Poland.

Why it mattered: New borders created minority problems—ethnic groups often ended up inside states they did not identify with, generating grievances that destabilized the region.

Military restrictions

Germany faced limitations on its armed forces and military capabilities.

Why it mattered: Restrictions aimed to reduce German threat, but they also became symbols of humiliation and fueled revisionist politics.

Reparations and “war guilt”

Germany was required to accept responsibility for the war in the treaty’s terms (often referenced through the “war guilt” clause, Article 231) and to pay reparations.

How it worked politically: Reparations became a lightning rod. Even when economists and politicians debated what Germany could realistically pay, the very existence of reparations fed anger and the belief that the peace was punitive.

Common misconception: The treaty alone did not “cause WWII” in a simple, mechanical way. It created conditions—resentment, economic strain, diplomatic conflict—that later leaders could exploit.

The wider peace settlement (beyond Versailles)

AP questions sometimes reward you for recognizing that “Versailles” is shorthand for multiple treaties.

• Treaty of Saint-Germain (1919) addressed Austria.
• Treaty of Trianon (1920) addressed Hungary.
• Treaty of Neuilly (1919) addressed Bulgaria.
• The Ottoman Empire was also forced into postwar treaties, later revised (with Lausanne (1923) replacing the earlier settlement after Turkish resistance).

Why it matters: The breakup of empires created many new borders and disputes. The settlement was not just about Germany.

The League of Nations: idealism and limitations

The League of Nations was created to promote collective security and prevent future wars.

• In theory, aggressors would face united opposition.
• In practice, enforcement was difficult because the League depended on member states’ willingness to act.

The League’s limitations are important because they reveal a central interwar problem: states wanted peace, but many were unwilling to pay the costs of enforcing it.

Effects on Europe: instability, resentment, and new political movements

The settlement reshaped Europe in at least four major ways.

1) German resentment and revisionism

Many Germans viewed the treaty as a “dictated peace.” This sentiment did not require everyone to support extremism, but it created a broad political vulnerability that anti-democratic movements could exploit later.

2) New states, minority conflicts, and border tensions

The map of Europe changed dramatically. But the principle of self-determination collided with reality: mixed ethnic settlement patterns meant that drawing “fair” borders was nearly impossible.

3) Economic strain and political radicalization

Postwar economies faced debt, reconstruction costs, and social dislocation. Economic hardship can strengthen radical politics by making moderate compromise seem ineffective.

4) A new but fragile international order

The postwar order tried to replace secret alliances and balance-of-power politics with international institutions and norms. Yet many old habits remained, and the enforcement mechanisms were weak.

Worked example: a thesis that earns points

A strong LEQ/DBQ-style thesis about the settlement might look like this:

The Versailles Settlement attempted to secure peace through German military restriction and new international institutions, but its punitive elements and the redrawing of borders created lasting instability. By humiliating Germany while also producing minority conflicts in Eastern Europe, the settlement undermined legitimacy and fostered revisionist and extremist politics in the interwar period.

Notice the structure: it states what the settlement tried to do, then explains multiple mechanisms for why it struggled.

Exam Focus

• Typical question patterns
  • Evaluate the extent to which the Versailles Settlement achieved the goals of security and self-determination.
  • Analyze how the peace settlement contributed to political instability in Germany and/or Eastern Europe.
  • Compare different national perspectives on the treaty (French security concerns vs. British imperial interests vs. Wilsonian idealism).
• Common mistakes
  • Treating “Versailles” as only the Treaty of Versailles; broader treaties and the breakup of empires often matter.
  • Oversimplifying causation by saying “Versailles caused WWII” without explaining intermediate steps (economic problems, political radicalization, revisionism, diplomatic failures).
  • Ignoring minority issues and focusing only on Germany, missing a major theme of interwar instability.