Causes of the Second World War

Introduction

The Second World War (1939–1945) was the most extensive and destructive armed conflict in modern history. It involved major powers and states across Europe, Asia, Africa, and the Pacific. Millions of military personnel and civilians lost their lives, cities and economies were devastated, and the international balance of power was transformed.

The war emerged from a combination of long-term structural problems and immediate political decisions. The unresolved consequences of the First World War, the weaknesses of the Treaty of Versailles, the Great Depression, the rise of fascism and militarism, aggressive expansionism, and the failure of collective security all contributed to the crisis.

However, the causes of the war cannot be explained without considering the decisions of political leaders, particularly Adolf Hitler and the Nazi regime. German expansionism and the invasion of Poland in September 1939 triggered the European war, while Japanese expansion had already produced a major conflict in Asia.

1. The Unresolved Legacy of the First World War

The First World War ended in 1918, but its political and economic consequences continued to shape international relations.

The peace settlement reorganised Europe and imposed new borders, obligations, and restrictions on defeated states.

The Treaty of Versailles of 1919 placed responsibility for the war on Germany and imposed territorial losses, military restrictions, and reparations.

Germany lost territory in Europe and its overseas colonies. Its armed forces were severely restricted, and the Rhineland was demilitarised.

Many Germans regarded the treaty as humiliating and unjust. This resentment became an important source of nationalist mobilisation.

The post-war settlement therefore failed to create a durable sense of legitimacy among several important states.

2. The Treaty of Versailles and German Resentment

The Treaty of Versailles was intended to weaken Germany militarily and prevent renewed aggression.

Its major provisions included:

• Territorial losses.
• Restrictions on the size of the German army.
• Prohibition of compulsory military service.
• Restrictions on the navy and prohibition of submarines.
• Prohibition of military aircraft and tanks.
• Demilitarisation of the Rhineland.
• Reparations obligations.

The treaty contributed to resentment among German nationalists, who portrayed it as a dictated peace.

Hitler exploited this dissatisfaction by promising to restore German military power, recover lost territories, and reverse the post-war settlement.

Nevertheless, the treaty alone does not explain the war. German expansionism resulted from deliberate political and ideological choices that went beyond the revision of Versailles.

3. Rise of Fascism and Nazism

The interwar period witnessed the growth of authoritarian and totalitarian political movements.

Italian Fascism under Benito Mussolini promoted extreme nationalism, militarism, authoritarian leadership, and imperial expansion.

In Germany, Adolf Hitler and the Nazi Party developed an even more radical ideology based on racial hierarchy, antisemitism, authoritarian rule, territorial expansion, and the idea of Lebensraum, or living space.

The Nazi regime rejected liberal democracy and international cooperation based on equality among states.

Its foreign policy aimed to establish German dominance in Europe and acquire territory, particularly in Eastern Europe.

The rise of these regimes transformed international relations by making military expansion and ideological confrontation central features of state policy.

4. The Great Depression

The Great Depression began in 1929 and produced a worldwide economic crisis.

Unemployment, industrial decline, banking failures, and falling international trade weakened democratic governments and increased social unrest.

Germany was particularly vulnerable because its economic recovery depended partly on foreign loans and international financial cooperation.

The crisis strengthened the Nazi Party, which promised employment, economic recovery, national unity, and restoration of German power.

Economic hardship also encouraged protectionism and competition for resources, markets, and influence.

Although the Great Depression did not automatically cause war, it weakened democratic institutions and created favourable conditions for extremist political movements.

5. Failure of the League of Nations

The League of Nations was established to maintain international peace through collective security and peaceful dispute settlement.

However, it lacked the military and political strength to prevent aggression by major powers.

Its failures became particularly evident during three major crises:

• Japan’s occupation of Manchuria in 1931.
• Italy’s invasion of Ethiopia in 1935.
• Germany’s remilitarisation of the Rhineland in 1936.

The League’s inability to enforce international agreements encouraged aggressor states to believe that expansion could succeed without facing serious consequences.

The collapse of collective security weakened the foundations of the post-war international system.

6. Aggressive Expansionism

The expansionist policies of Germany, Italy, and Japan were among the most immediate causes of the war.

6.1 German Expansionism

Hitler sought to overturn the Treaty of Versailles, unite German-speaking populations, and expand German territory.

Germany remilitarised the Rhineland in 1936, annexed Austria in 1938, acquired the Sudetenland through the Munich Agreement, and occupied the remaining Czech lands in March 1939.

These actions progressively destroyed the European settlement established after the First World War.

6.2 Italian Expansionism

Mussolini sought to establish an Italian empire and expand Italian influence in Africa and the Mediterranean.

Italy invaded Ethiopia in 1935 and occupied Albania in 1939.

These actions weakened international security and brought Italy into closer alignment with Nazi Germany.

6.3 Japanese Expansionism

Japan pursued territorial expansion in East Asia and the Pacific.

It occupied Manchuria in 1931 and launched a full-scale invasion of China in 1937.

Japanese expansion challenged Western interests and contributed to the widening of international conflict in Asia.

7. Militarism and the Arms Race

Militarism was an important feature of international politics during the 1930s.

Germany expanded its army, established the Luftwaffe, and developed modern weapons and military organisations.

Italy increased military spending and pursued imperial campaigns, while Japan strengthened its armed forces and expanded naval capabilities.

The failure of disarmament initiatives encouraged states to prioritise military preparedness over international cooperation.

The growing arms race increased suspicion, strengthened aggressive regimes, and made the use of force more likely.

8. Appeasement

Appeasement was primarily pursued by Britain and France during the 1930s.

The policy involved making concessions to Hitler in the hope of preventing another European war.

Its supporters believed that some German grievances were legitimate and that negotiation could produce a stable settlement.

However, the concessions enabled Germany to strengthen its strategic position.

The Munich Agreement of September 1938 allowed Germany to occupy the Sudetenland. In March 1939, Hitler occupied the remaining Czech lands, demonstrating that his ambitions were not limited to the unification of German-speaking populations.

Appeasement failed to restrain German expansion and weakened confidence in international agreements.

9. The Spanish Civil War and International Polarisation

The Spanish Civil War (1936–1939) became an international confrontation involving competing ideological and strategic interests.

Germany and Italy supported Franco’s Nationalist forces, while the Soviet Union assisted the Republicans.

Britain and France pursued non-intervention, but the agreement was not effectively enforced.

The conflict strengthened cooperation between Germany and Italy and demonstrated the increasing internationalisation of ideological disputes.

It also revealed the weakness of collective efforts to prevent military intervention.

10. The Nazi-Soviet Non-Aggression Pact

On 23 August 1939, Nazi Germany and the Soviet Union signed a non-aggression pact.

The agreement was unexpected because the two regimes were ideological opponents.

Its secret protocol divided parts of Eastern Europe into German and Soviet spheres of influence.

The pact reduced Hitler’s immediate concern about a two-front war and provided an opportunity to attack Poland.

It also demonstrated how strategic calculations could override ideological differences in international politics.

11. Immediate Cause: The Invasion of Poland

The immediate cause of the European war was Germany’s invasion of Poland on 1 September 1939.

Hitler had demanded changes concerning the Free City of Danzig and access through the Polish Corridor. These demands formed part of a broader campaign to weaken and dominate Poland.

Germany launched a military invasion using coordinated air and ground operations.

On 17 September, Soviet forces entered eastern Poland under the secret arrangements of the Nazi-Soviet Pact.

Britain and France had guaranteed assistance to Poland. After Germany refused to withdraw, both countries declared war on Germany on 3 September 1939.

The European war had begun.

12. Causes of the Wider Global Conflict

The war was not confined to Europe. The conflict in Asia had already developed through Japanese expansion into China.

Tensions between Japan and the United States increased because of Japanese military operations and the threat they posed to Western interests in the Pacific.

In December 1941, Japan attacked Pearl Harbor and launched simultaneous offensives against American, British, and Dutch territories.

The United States entered the war, transforming the European and Asian conflicts into a fully global struggle.

The European war and the Asian-Pacific war were interconnected, although they had distinct origins and developed through different sequences of events.

13. Long-Term and Immediate Causes: An Analytical Assessment

The causes of the Second World War can be divided into two broad categories.

Long-term causes:

• The unresolved consequences of the First World War.
• Resentment over the Treaty of Versailles.
• The rise of fascism, Nazism, and militarism.
• The Great Depression.
• The failure of collective security.
• Aggressive nationalism and imperial expansion.
• The international arms race.

Immediate causes:

• German occupation of Czechoslovakia in March 1939.
• The failure of diplomatic efforts to restrain Hitler.
• The Nazi-Soviet Pact of August 1939.
• German demands against Poland.
• The invasion of Poland on 1 September 1939.
• British and French declarations of war on 3 September 1939.

The distinction is important because long-term conditions created the environment for conflict, while immediate political decisions transformed the crisis into war.

Conclusion

The Second World War resulted from a complex interaction of historical grievances, economic crises, ideological extremism, militarism, territorial expansion, and diplomatic failure.

The Treaty of Versailles left unresolved tensions, while the Great Depression weakened democratic governments and strengthened extremist movements. The League of Nations failed to prevent aggression, and appeasement did not restrain Hitler.

The expansionist policies of Germany, Italy, and Japan progressively undermined international peace. The Nazi-Soviet Pact and Germany’s invasion of Poland finally triggered the European war, while Japanese expansion and the attack on Pearl Harbor brought the United States into the wider conflict.

The war demonstrates that international peace cannot be sustained through agreements alone. It requires legitimate institutions, political cooperation, effective deterrence, and a willingness to resist aggression.

Key Takeaways

1. The Second World War lasted from 1939 to 1945.
2. The First World War left unresolved political and territorial grievances.
3. The Treaty of Versailles created deep resentment in Germany.
4. Fascism and Nazism promoted authoritarianism, militarism, and expansionism.
5. The Great Depression weakened democratic institutions.
6. The League of Nations failed to prevent aggression.
7. Germany, Italy, and Japan pursued expansionist foreign policies.
8. German rearmament transformed the European balance of power.
9. Appeasement failed to restrain Hitler.
10. The Spanish Civil War strengthened international ideological divisions.
11. The Nazi-Soviet Pact was signed in August 1939.
12. Germany invaded Poland on 1 September 1939.
13. Britain and France declared war on Germany on 3 September 1939.
14. Japanese expansion had already produced a major war in Asia.
15. The attack on Pearl Harbor brought the United States into the global conflict.

Review Questions

1. What were the principal long-term causes of the Second World War?
2. How did the Treaty of Versailles contribute to international instability?
3. Explain the relationship between the Great Depression and the rise of Nazism.
4. How did fascism and militarism undermine international peace?
5. Why did the League of Nations fail to prevent aggression?
6. Discuss the expansionist policies of Germany, Italy, and Japan.
7. How did appeasement contribute to the outbreak of war?
8. What was the international significance of the Spanish Civil War?
9. Explain the purpose and consequences of the Nazi-Soviet Pact.
10. Why did Germany invade Poland in September 1939?
11. Distinguish between the long-term and immediate causes of the war.
12. How did the conflict in Asia become part of the wider Second World War?

Further Reading

• Encyclopaedia Britannica: World War II
• The National WWII Museum
• Imperial War Museums
• A. J. P. Taylor, The Origins of the Second World War.
• Ian Kershaw, To Hell and Back: Europe 1914–1949.
• Zara Steiner, The Triumph of the Dark: European International History 1933–1939.