Study Notes: Causes and Effects of 20th-Century Wars (World History Topic 11)

Hello future historians! This chapter is one of the most vital in the entire IB History curriculum. We are exploring the concept of causation (why wars happen) and consequence (what happens afterward) for the massive conflicts that defined the 20th century, from the World Wars to limited and civil conflicts.


Understanding these wars isn't just about memorizing dates; it’s about recognizing patterns, understanding human motives, and seeing how the echoes of one conflict immediately become the causes of the next. Don't worry if this seems tricky at first—we will break down the causes into simple, manageable categories!


Section 1: Defining 20th-Century Conflict

The 20th century saw warfare evolve dramatically, moving from traditional state-on-state battles to massive global conflicts and ideological proxy wars.

Types of Conflict Relevant to the Syllabus
  • Total War: Conflicts (like WWI and WWII) where distinction between combatants and civilians blurs, requiring total mobilization of a nation’s resources (economic, industrial, human).
  • Limited War: Conflicts where nations fight for specific objectives without committing all resources or attempting unconditional surrender (e.g., Korean War, Gulf War).
  • Civil War: Conflicts fought within the borders of a single state, often driven by ideological, ethnic, or political divisions (e.g., Spanish Civil War).
  • Proxy Wars: Conflicts where major powers support opposing sides in a limited war, often without fighting each other directly (common during the Cold War, like the Vietnam War).

Quick Review: When analyzing a war, always ask: How "total" was it? Who was the target? What were the defined aims?


Section 2: Analyzing the Causes of War (Causation)

Historians usually divide causes into two main categories: long-term causes (the underlying conditions and tensions that build over years) and short-term causes (the immediate crises or 'sparks' that ignite the conflict).

2.1. Long-Term Causes: The Pressure Cooker

Think of long-term causes as slowly heating water in a pressure cooker. The tension builds gradually until something finally makes the lid blow off.

We often use the acronym M.A.I.N. to remember the foundational causes of major global wars, especially WWI:

  • Militarism: The belief that a country should maintain a strong military capability and be prepared to use it aggressively. This led to dangerous arms races (especially between Britain and Germany before 1914).
  • Alliance Systems: Complex, rigid networks of treaties that guaranteed if one nation was attacked, its allies would join the fight. This turned small disputes into massive conflicts (e.g., the Triple Entente vs. the Triple Alliance).
  • Imperialism: Competition between European powers to build vast empires overseas, leading to conflicts over resources and territory in Africa and Asia (economic rivalry).
  • Nationalism: Extreme pride in one's nation, often coupled with the desire for self-rule or superiority over others. This was a major destabilizing force in regions like the Balkans.

Did you know? In the lead-up to WWI, the extensive railway mobilization timetables meant that military leaders felt they couldn't risk partial mobilization—it had to be all or nothing. This accelerated the commitment to war once the crisis began.

2.2. Short-Term Causes: The Spark

The short-term cause is the specific event that sets the long-term causes into motion.

  • WWI Trigger: The assassination of Archduke Franz Ferdinand in Sarajevo (June 1914).
  • WWII Trigger: Germany's invasion of Poland (September 1939).

Accessibility Tip: Avoiding the Common Pitfall

A major common mistake is confusing the trigger with the root cause. Franz Ferdinand's assassination did not *cause* WWI; it was the *excuse* that allowed the existing long-term tensions (M.A.I.N.) to explode. The Treaty of Versailles did not *cause* WWII, but the resentment and economic collapse it fostered were critical long-term causes allowing Hitler's rise.


Section 3: Case Studies in 20th-Century Causation

While the M.A.I.N. framework works well for WWI, subsequent wars often involve different mixes of factors, especially Ideology (Fascism, Communism) and the breakdown of international cooperation.

3.1. The Road to World War II (Failure of Consequence)

The causes of WWII are often direct consequences of WWI.

  • Resentment and Revisionism (Germany/Italy/Japan): The Treaty of Versailles (1919) created deep resentment, particularly in Germany (war guilt clause, massive reparations), leading to the rise of leaders like Hitler who promised to "revise" the treaty's terms.
  • Expansionism and Ideology: The aggressive, expansionist foreign policies of Authoritarian States (Topic 10 overlap) in Germany (Nazism), Italy (Fascism), and Japan (Militarism).
  • Economic Instability: The Great Depression (1929) destabilized global politics, making extreme ideologies more appealing and promoting protectionism over global cooperation.
  • Failure of Collective Security: The inability of the League of Nations (the post-WWI international body) to enforce peace, notably failing to stop Japanese aggression in Manchuria (1931) or Italian aggression in Abyssinia (1935).
  • Appeasement: The policy followed by Britain and France of making concessions to aggressive powers (like Hitler) in hopes of maintaining peace, which only emboldened them (e.g., Munich Agreement, 1938).

Key Takeaway for Causation: WWI was caused by rigid systems and competing empires. WWII was caused by the failure to resolve the consequences of WWI, coupled with aggressive ideology and economic collapse.


Section 4: The Profound Effects of War (Consequence)

Wars are powerful engines of change. The effects of 20th-century conflicts profoundly restructured the global order. Remember to analyze effects across multiple dimensions: political, economic, social, and technological.

4.1. Political and Ideological Consequences

The greatest political consequence of the 20th-century wars was the complete redrawing of the global map and the shift in power balance.

  • End of Empires (Post-WWI & WWII): WWI destroyed the Russian, Austro-Hungarian, Ottoman, and German Empires. WWII led directly to the acceleration of decolonization as European powers were too weak to hold onto their colonies.
  • Rise of Superpowers: Post-WWII, the US and the USSR emerged as the dominant global powers, leading directly into The Cold War (Topic 12 overlap) and a bipolar world.
  • Establishment of International Organizations:
    • After WWI: The League of Nations (a major failure, demonstrating the need for better mechanisms).
    • After WWII: The United Nations (UN) (designed to be more robust than the League, with a permanent Security Council).
  • Ideological Shifts: The rise and eventual defeat of Fascism, and the global struggle between Capitalism and Communism.
4.2. Social and Demographic Consequences

The human cost was staggering, leading to massive social changes.

  • Demographic Loss: Tens of millions of casualties (military and civilian). WWI created the "lost generation" in Europe; WWII introduced industrial genocide (the Holocaust).
  • Role of Women: Women took on traditionally male roles in industry and agriculture during both World Wars, strengthening arguments for political equality (leading to increased rights and protest—Topic 4 overlap).
  • Mass Displacement: Millions became refugees, leading to ethnic conflicts and boundary disputes, especially in Europe post-WWII and in regions undergoing decolonization.
  • Psychological Trauma: Widespread psychological effects (shell shock in WWI, PTSD in subsequent conflicts).
4.3. Economic and Technological Consequences
  • Debt and Recovery: Most European powers were bankrupted by the World Wars. The US emerged as the dominant economic power. Post-WWII reconstruction efforts (like the Marshall Plan) solidified the Western economic alliance.
  • Innovation: Warfare drove rapid technological advancements in aviation, rocketry (leading to the space race), medicine, and nuclear physics (the Atomic Age).
  • Shift to Command Economies (for war): Both World Wars necessitated massive state intervention and central planning (war socialism/economic mobilization).

Analogy: Think of the consequences of WWI and WWII like a domino effect. The failure of the first domino (the Treaty of Versailles) set up the second and third (WWII and the Cold War).


Section 5: Causes and Effects of Limited and Civil Wars

Not all 20th-century wars were global. In limited and civil wars, the factors of causation are often more localized, revolving around decolonization, internal ethnic tension, or superpower interference (proxy fighting).

5.1. Limited/Proxy War Causation (e.g., Korea, Vietnam)
  • Cold War Ideology: The primary driver was the ideological conflict between the US and USSR, who sought to gain influence without direct, open conflict (containment and domino theory).
  • Decolonization Vacuum: In places like Vietnam, the withdrawal of the former colonial power (France) left a power vacuum, which was filled by competing nationalist and ideological factions.
  • Local Nationalism: While Cold War powers funded the fight, the local populations were often driven by intense national identity and the desire for unification (e.g., Ho Chi Minh in Vietnam).
5.2. Effects of Limited/Proxy Wars

The effects of limited wars were often geographically contained but locally devastating.

  • Massive Local Destruction: Despite being "limited" globally, wars like Vietnam resulted in catastrophic environmental and human costs in the affected region.
  • Psychological Defeat: For superpowers, limited wars could lead to significant internal political crises and loss of morale (e.g., US withdrawal from Vietnam).
  • Creation of New States/Borders: Limited wars often solidified existing political divisions (e.g., the continued division of Korea).

Quick Review Box: Mastering Causation and Consequence

To succeed in essay writing on this topic, ensure your arguments always link causation and consequence:

Causation Focus: Identify *multiple* long-term factors (M.A.I.N., economic rivalry, ideological difference) and relate them to the *single* short-term trigger.

Consequence Focus: Do not just list outcomes; categorize them (Political, Social, Economic) and discuss their *significance* (e.g., the *significance* of the UN's creation was the attempt to create a structured system of collective security, a direct response to the *failure* of the League).

IB Concept Connection: Emphasize that the consequences of one war inevitably become the causes of the next global crisis (WWI consequences leading to WWII causes).