AP World History: Modern — World War I and the Interwar Order (Unit 7.1–7.4)

Shifting Power After 1900

A world that was already changing before 1914

By 1900, the global balance of power looked stable on the surface—large empires controlled vast territories—but underneath, it was increasingly fragile. Shifting power after 1900 refers to how industrial capacity, imperial rivalries, rising nationalism, and new military technologies changed which states had leverage and how quickly a regional crisis could become a global war.

What makes this period important is that World War I didn’t “come out of nowhere.” It grew out of a system where major powers were tightly connected through diplomacy, trade, colonial competition, and security commitments. When that system faced a shock, the connections acted less like safety nets and more like tripwires.

The “Great Power” system and why it was unstable

Europe’s Great Powers—especially Britain, France, Germany, Austria-Hungary, Russia, and (increasingly) Italy—saw security as a competitive, zero-sum issue. If your rival grew stronger, you felt weaker, even if your own country hadn’t changed.

Several long-term forces made instability worse:

• Industrialization and military capacity: Industrial output translated into weapons, railroads, and the ability to mobilize huge armies. Germany’s rapid industrial growth after unification (1871) changed the strategic map—neighbors recalculated what “survival” required.
• Imperial competition: Empires weren’t only about profits; they were also about prestige and strategic advantage (naval bases, chokepoints, raw materials). Colonial rivalries increased distrust in Europe.
• Nationalism: Nationalism (loyalty to a shared identity like language, culture, or history) could unify states (Germany, Italy) but also fracture multiethnic empires (Austria-Hungary, Ottoman Empire). In places like the Balkans, nationalist movements made local conflicts more explosive.

A common misconception is to treat imperialism and nationalism as separate causes that you simply list. In reality, they interacted: imperial competition raised tensions among Great Powers, while nationalism created flashpoints (especially where empires ruled diverse peoples).

Militarism and the security dilemma

Militarism is more than “having an army.” It is the belief that military strength is essential to national power and that war is an acceptable (even normal) tool of policy. After 1900, many states invested heavily in armaments and war planning.

A key mechanism here is the security dilemma: when one state arms to feel safe, rivals interpret that as a threat and arm too—making everyone less safe. This matters because it turns “preparation” into escalation.

Example: The Anglo-German naval arms race

Britain relied on naval supremacy to protect its empire and trade routes. Germany, seeking greater world influence, built a stronger navy. Britain responded by expanding and modernizing its fleet (including the “Dreadnought” battleship). Each side claimed it was acting defensively, but the outcome was rising hostility and fear.

Alliances as deterrence that can become a trap

By the early 1900s, European diplomacy had hardened into two broad alliance systems:

• Triple Alliance (Germany, Austria-Hungary, Italy)
• Triple Entente (France, Russia, Britain)

Alliances can deter aggression if everyone believes a war would be too costly. But they can also create entangling commitments: if one member is threatened, others feel compelled to join, or risk losing credibility and security.

This is one of the most tested ideas in AP World: the same alliance system that was supposed to prevent war also helped spread a crisis across the continent.

Declining empires and rising pressures

Even before WWI, several empires faced internal strain:

• Ottoman Empire: weakening control over territories; nationalist movements in the Balkans challenged Ottoman authority.
• Austria-Hungary: multiple ethnic groups with competing nationalisms; governance required delicate compromise.
• Russia: industrializing unevenly, facing unrest and revolutionary movements.

The Balkans became a key “pressure point” because it combined declining imperial control, rising nationalism (including Pan-Slavism), and Great Power rivalry.

Exam Focus

• Typical question patterns:
  • Explain how nationalism and imperialism created instability in the early 1900s.
  • Compare the causes of WWI to those of another conflict (often focusing on alliances, militarism, or competition for territory).
  • Use a stimulus (map of alliances, political cartoon, arms production chart) to argue why tensions escalated.
• Common mistakes:
  • Treating alliances as a single “cause” without explaining the mechanism (how they spread a crisis).
  • Ignoring the Balkans and focusing only on western Europe.
  • Writing “militarism caused war” without connecting militarism to arms races, war plans, or the security dilemma.

Causes of World War I

The difference between long-term causes and a short-term trigger

When historians explain World War I, they usually separate:

• Long-term causes: underlying conditions that made war more likely (militarism, alliances, imperialism, nationalism).
• Immediate trigger: the event that set the system in motion.

This distinction matters because AP questions often ask you to evaluate causation: not just what happened, but why some factors mattered more than others.

The assassination at Sarajevo and why it escalated

The immediate trigger was the assassination of Archduke Franz Ferdinand (heir to Austria-Hungary) in Sarajevo on June 28, 1914, by Gavrilo Princip, a Bosnian Serb nationalist connected to networks sympathetic to Serbian nationalist goals.

On its own, an assassination does not automatically cause a world war. It escalated because leaders interpreted it through the lens of fear, prestige, and alliance commitments.

How escalation worked: the July Crisis (step-by-step)

Think of the July Crisis as a rapid chain reaction where each step narrowed the options for peace.

1. Austria-Hungary blamed Serbia (at least indirectly) and wanted to crush Serbian influence to preserve the empire.
2. Germany supported Austria-Hungary (often described as giving a “blank check”), encouraging a hard line.
3. Austria-Hungary issued an ultimatum to Serbia with severe demands.
4. Serbia accepted some demands but not all; Austria-Hungary declared war.
5. Russia mobilized to support Serbia (partly due to Pan-Slavism and strategic interests).
6. Germany declared war on Russia and then on France (Russia’s ally).
7. Germany’s invasion of Belgium (to reach France quickly) brought Britain into the war.

A key misconception is that “alliances automatically forced war.” In reality, leaders made choices at each step—but they made them under intense pressure created by alliances, mobilization schedules, and expectations of a short war.

Nationalism: unifying and destabilizing

Nationalism mattered at multiple levels:

• In Serbia and among South Slavs, nationalism was tied to independence and unification.
• In Austria-Hungary, nationalism was a threat: if one group gained independence, others might follow.
• In France, nationalism included the desire to recover Alsace-Lorraine (lost to Germany in 1871), shaping rivalry with Germany.

Nationalism was not only about pride; it could be a political tool. Leaders used nationalist rhetoric to build support and justify aggressive policies.

Imperialism and global competition

Imperial rivalries increased suspicion and hostility, even if they weren’t the direct spark in 1914. Crises in places like Morocco (involving France and Germany) heightened distrust and made it harder for leaders to believe rivals were acting in good faith.

In AP writing, it’s stronger to say: imperial competition made diplomacy more brittle and intensified rivalries—so when the Balkan crisis hit, cooperation was less likely.

Militarism, war plans, and the “use it or lose it” problem

Militarism wasn’t just cultural enthusiasm for the military; it also lived in institutions:

• General staffs developed rigid mobilization plans.
• Railroads and timetables made partial mobilization difficult.
• Leaders feared that delaying mobilization could be fatal.

This created a “use it or lose it” logic: once mobilization began, it was hard to stop without appearing weak or risking defeat.

Example: Turning a Balkan war into a continental war

A limited conflict between Austria-Hungary and Serbia might have stayed regional if Great Powers had restrained allies. But Russia’s mobilization signaled that the conflict could expand; Germany responded according to its war plans; France and Britain entered due to alliance ties and the invasion of Belgium.

Exam Focus

• Typical question patterns:
  • Evaluate the relative importance of two causes (for example, nationalism vs. alliances) in leading to WWI.
  • Use documents (speeches, mobilization orders, propaganda) to explain how leaders justified war.
  • Explain how a regional event became a global conflict.
• Common mistakes:
  • Listing “M.A.I.N.” (militarism, alliances, imperialism, nationalism) without explaining how each one contributed.
  • Treating the assassination as “the cause” rather than a trigger within a tense system.
  • Ignoring agency by implying war was inevitable; AP essays often reward nuanced causation.

Conducting World War I

What made WWI a “modern” war

World War I was fought with industrial-era technologies and mass armies, producing levels of destruction that shocked contemporaries. Calling it “modern” doesn’t mean everything was new; it means warfare was shaped by industrial production, rapid communication, and the ability to equip millions of soldiers.

This matters because how the war was conducted affected outcomes at home and abroad: governments expanded power, economies were redirected toward war production, and societies experienced trauma that influenced interwar politics.

Trench warfare and the stalemate on the Western Front

On the Western Front (notably France and Belgium), armies dug extensive trench systems. Trench warfare developed because:

• Defensive firepower (machine guns, rapid-firing artillery) made frontal assaults extremely costly.
• Barbed wire and fortifications slowed advances.
• Commanders often believed they could “break through” with one more push, leading to repeated offensives with limited gains.

A misconception to avoid: trench warfare was not everywhere. The war also had mobile fronts and different conditions in Eastern Europe, the Middle East, and Africa.

Example: Why “no one could win quickly” in the West

If both sides can produce shells, replace troops, and defend with machine guns, then attacking becomes much harder than holding. That basic imbalance helps explain years of stalemate.

War beyond the trenches: multiple theaters

While the Western Front dominates memory, WWI was a global conflict:

• Eastern Front: generally more movement than the West, involving Germany, Austria-Hungary, and Russia.
• Ottoman fronts: fighting in the Middle East; the Ottoman Empire joined the Central Powers.
• Colonial theaters: battles occurred in Africa and Asia; colonies provided troops and resources.

Showing global breadth is a strong AP skill: it connects European decisions to worldwide imperial systems.

New technologies and their effects

Industrial warfare introduced or expanded the use of:

• Machine guns and heavy artillery: increased casualties and strengthened defense.
• Poison gas: caused terror and injury; its battlefield impact varied but its psychological impact was enormous.
• Tanks: developed to cross trenches and barbed wire; early models were unreliable but signaled changing tactics.
• Airplanes: used for reconnaissance and later combat; improved coordination and targeting.
• Submarines (U-boats): Germany used unrestricted submarine warfare to disrupt shipping, contributing to the entry of the United States.

The key idea is not “technology caused victory,” but “technology changed the cost and character of fighting,” pushing states toward total mobilization.

Total war: mobilizing entire societies

Total war means war that requires the mobilization of an entire society’s people, economy, and politics—not just the army. Governments expanded authority to:

• direct industrial production (weapons, uniforms, ships)
• ration food and resources
• control information through censorship and propaganda
• conscript soldiers and organize labor

This matters because total war blurs the line between battlefield and home front. Civilians became more directly involved and more directly targeted through blockades and shortages.

Example: The home front and changing gender roles

With millions of men mobilized, women in many countries entered industrial and agricultural work in larger numbers. It’s tempting to claim WWI “created” women’s rights everywhere, but the more accurate point is: the war accelerated changes already underway and gave new arguments for political inclusion in some places.

Propaganda and public opinion

Governments used propaganda to maintain morale, encourage enlistment, justify sacrifice, and portray enemies as threats to civilization. Understanding propaganda helps you analyze WWI sources: posters, speeches, and newspaper accounts often reflect state goals more than objective reality.

A common mistake on document-based questions is to quote propaganda as if it were factual reporting. Instead, you should ask: who made it, for what audience, and what behavior did they want?

The war’s turning points and the end of fighting

Several developments reshaped the conflict:

• United States entry (1917): The U.S. joined the war on the Allied side after factors including German unrestricted submarine warfare and the Zimmermann Telegram. U.S. manpower and resources strengthened the Allies.
• Russia’s withdrawal (1917–1918): The Russian Revolution led to Russia leaving the war (Treaty of Brest-Litovsk, 1918). This allowed Germany to shift forces west, but also reflected internal collapse.
• Armistice (November 11, 1918): Fighting ended with an armistice, not an immediate peace treaty.

The peace settlement and why it mattered for the “aftermath”

The war ended with peace negotiations that redrew borders and created new states, especially in Eastern Europe. The most famous settlement was the Treaty of Versailles (1919) with Germany. Broadly, the postwar settlement:

• assigned blame and imposed penalties (including reparations) on Germany
• rearranged territories and created mandates
• helped establish the League of Nations (though the U.S. never joined)

The important historical point is that the settlement tried to balance punishment, security, and self-determination—and often satisfied none fully. This set up instability in the interwar period.

Exam Focus

• Typical question patterns:
  • Explain how industrialization affected the conduct of WWI (technology, total war, civilian involvement).
  • Compare experiences of soldiers or civilians in different theaters (Western Front vs. Ottoman front, for example).
  • Analyze how participation in WWI affected colonial subjects (troop contributions, promises, postwar expectations).
• Common mistakes:
  • Claiming trenches explain all of WWI (ignoring other fronts and naval warfare).
  • Treating propaganda sources as neutral facts instead of strategic messaging.
  • Describing total war as “everyone fought” rather than “the state reorganized society and the economy for war.”

Economy in the Interwar Period

Why the interwar economy was fragile

The interwar period (the years between WWI and WWII) was economically unstable because the war had disrupted trade, destroyed infrastructure in parts of Europe, and left governments with huge debts. The global economy was increasingly interconnected—so problems in one major economy could spread.

This topic matters in AP World because economic crisis helps explain political radicalization, the weakening of democratic systems in some states, and the appeal of extremist or authoritarian solutions.

War debts, reparations, and the problem of rebuilding

After WWI, many European countries faced:

• War debts: Governments borrowed heavily to finance total war.
• Reparations: Payments demanded from Germany, especially under the Treaty of Versailles.
• Reconstruction costs: Rebuilding damaged regions and restarting production.

The key mechanism is that these burdens were linked across borders. If Germany struggled to pay reparations, France and Britain (who expected reparations) had more difficulty repaying debts to the United States. This created a tense financial chain.

A misconception to avoid: reparations alone did not “cause” the Great Depression. They contributed to instability, but the Depression had broader global causes.

Inflation and social consequences

Some countries experienced severe inflation as governments printed money to meet obligations. Germany’s hyperinflation in the early 1920s became a symbol of chaos and humiliation for many Germans.

Economically, inflation destroys savings and makes wages unpredictable. Politically, it can delegitimize governments and make radical movements more appealing because people begin to doubt that normal politics can protect them.

Example: How inflation becomes a political problem

If your savings become worthless, you may blame the current government, outsiders, or the entire political order. That emotional and social impact is part of why economic conditions can reshape ideology.

The Great Depression as a global turning point

The Great Depression began after the 1929 stock market crash in the United States, but it became a global depression because international trade and finance were tightly connected.

You should focus on what makes a depression different from a normal downturn:

• widespread bank failures and credit contraction
• collapsing demand (people and businesses stop spending)
• mass unemployment
• declines in global trade

The Depression mattered for world history because it weakened faith in liberal capitalism and helped push many states toward stronger government intervention or authoritarian alternatives.

Government responses: liberalism, Keynesian ideas, and state intervention

Governments responded in different ways, but a general trend was expanded state involvement in the economy.

• Some states adopted policies associated with Keynesian thinking (the idea that government spending can help stimulate demand during downturns). In the United States, the New Deal expanded federal programs and public works.
• Other governments pursued austerity or tried to maintain the gold standard longer, which in some cases worsened unemployment and political dissatisfaction.

You don’t need to memorize every policy detail to do well on AP questions; you do need to explain the logic: when private demand collapses, governments may step in to stabilize banks, create jobs, or regulate markets.

Protectionism and the breakdown of global trade

Many countries raised tariffs and restricted imports to protect domestic industries and jobs. The United States’ Smoot-Hawley Tariff (1930) is a well-known example.

Protectionism often seems intuitive—“buy local, protect workers”—but it can backfire internationally:

• other countries retaliate with their own tariffs
• global trade shrinks
• export industries collapse

This matters because shrinking trade intensified global tensions and encouraged some states to seek resources through imperial expansion.

Economic instability and the rise of extremist politics

Economic crisis does not automatically produce dictatorship, but it can create conditions where authoritarian movements gain support by promising order, jobs, and national revival.

In several cases, leaders framed economic recovery as requiring:

• stronger executive authority
• reduced labor organizing and political opposition
• nationalist unity against internal “enemies” or foreign exploitation

In AP World, it’s important to connect economics to ideology carefully. Avoid oversimplifying into “the Depression caused fascism.” A more accurate causal chain is: severe economic suffering undermined trust in existing institutions, making radical solutions more appealing.

Example: Linking economics to foreign policy

When international trade collapses and access to raw materials feels uncertain, states may pursue economic self-sufficiency or territorial expansion. This helps explain why the interwar economic order is connected to later global conflict.

Exam Focus

• Typical question patterns:
  • Explain how WWI financial arrangements (debts and reparations) contributed to instability in the 1920s.
  • Analyze causes and effects of the Great Depression using a graph or data on unemployment/trade.
  • Compare state responses to economic crisis (market regulation, public works, protectionism).
• Common mistakes:
  • Attributing the Great Depression to a single cause (AP readers reward multi-causal explanations).
  • Forgetting the global dimension by writing only about the United States.
  • Treating protectionism as purely helpful without explaining retaliation and declining trade.