7.2B: Causes of WWI

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Learning Objective 2B

Explain the causes and consequences of World War I.

Historical Development 1

The causes of World War I included imperialist expansion and competition for resources. In addition, territorial and regional conflicts combined with a flawed alliance system and intense nationalism to escalate the tensions into global conflict.


The first decade of the 20th century saw European industrialized nations at peak power. Their colonial political power expanded across the world’s continents, and their global economic dominance was nearly absolute. But the same ingredients that had led to European success in the previous 200 years would now become the undoing of Europe as the nations of the continent exploded a world war. At the end of WWI, Europe lay in ruins with millions dead.  

World War I

World War One began on July 28, 1914. This war was unlike any fought in history. While most of the fighting took place in Europe, European colonizers required their colonies in Asia and Africa into the war effort. Colonies were relied upon to provide cheap raw materials and resources for the European war effort and soldiers for European armies. World War I was the first large-scale industrial war—and they produced death on an industrial scale. By 1918, tens of millions of soldiers and citizens had been killed by the conflict directly and indirectly.


July 28, 1914 – November 11, 1918


Most of the fighting took place in Europe, Italy, the Ottoman Empire. There were two main fronts of the war. The eastern was in eastern Europe on the land between the Axis Powers of Germany and Austria-Hungary and Allied Power Russia. At the same time, the Central and Axis Powers fought on the western front on the land between Germany and France.


There were two main alliances in WWI. The Central Powers of Austria-Hungary, Germany, and the Ottoman Empire. The Allied Powers were England, France, Italy, and Japan. The Central and Allied Powers forced their colonies to provide resources and soldiers for the war effort. The United States joined the war on the side of the Allies in 1917.


WWI was a  war primarily fought in Europe. Because European powers forced their colonies to send soldiers and raw materials for the war effort, it is considered history’s first global war. America’s entrance into the war in 1917 and more minor battles outside of Europe also added to the war’s global nature.


The Allies and the Central powers fought for control of Europe and over colonies.


The war ended with an Allied victory and the breaking up of the German Empire, the Austro-Hungarian Empire, and the Ottoman Empire. German colonies transferred to other countries, and the British and French extended their influence over the Middle East. 

The Central and Allied powers 

The Central Powers

  • German Empire and colonies
  • Austria-Hungary
  • The Ottoman Empire
  • Bulgaria (from 1915)

The Allied Powers

  • France and its colonies
  • The United Kingdom and its colonies (Canada, Australia, India, New Zealand, and South Africa)
  • The Russian Empire
  • Serbia
  • Belgium
  • Japan
  • Italy
  • The United States (from 1917)
  • China (from 1917)
  • Portugal (from 1916)
  • Greece (from 1917)

The causes of World War I

The causes of World War I were complex. They were a combination of complex relationship dynamics between European powers. Below are the most commonly cited reasons for the war.

Cause 1: Mutual defense alliances

Mutual defense alliances are agreements signed between nations that pledge allies to help each other militarily if one of the alliance members is attacked. During the 19th century, European countries signed a complex network of defense alliances. In some instances, these defense alliances between nations were kept secret from other nations, further complicating the relationships between European countries. Following the assassination of the Austrian Archduke Franz Ferdinand by a Serbian nationalist, Austria-Hungary invaded Serbia, setting off the European alliance system.

How the alliance system brought all of Europe into war

1. Austria-Hungary declared war on Serbia.

2. Serbia’s ally Russia mobilized its troops but did not declare war.

3. Austria-Hungary ally Germany declared preemptive war on Russia.

4. Russia’s ally France did not immediately declare war, but Germany invaded them in a preemptive attack.

5. England joined the war to support France.

Cause 2: Imperialism

By the early 20th century, European powers had colonized most of Africa and Asia. Japan also expanded in Asia when it invaded Korea in 1910. Emerging European powers such as Italy and Germany worried that English and French colonial expansion would continue to expand their power and influence. European nations began to use colonies and spheres of influence to settle scores with their European neighbors. Diplomatic conflicts increased between European countries over the few remaining areas of potential colonial influence. 

Cause 3: Nationalism

Nationalism is an extreme form of patriotism that celebrates one’s own culture above the culture of other groups or nations. Nationalism impacted the start of WWI in multiple ways.

  • First, nationalism resulted in the unification of Italian and German kingdoms into the unified states of Italy and Germany in 1871. These two new states destabilized the power balance of Europe.
  • Second, nationalism increased imperialism as Europeans sought new colonies, which they considered essential for maintaining great power status. In the Eastern European Balkan region, nationalists fought for the independence of their nations. Gavrilo Princip, who assassinated the Austrian Archduke, was a Serbian nationalist from the nationalist group the Black Hand.

Cause 4: Militarism

Militarism is when nations overemphasize the role of the military in their societies. Militarized societies often glorify military combat and spend excessive money arming the military. The decades leading up to WWI saw a massive military buildup within Europe. By 1910, the great powers of Europe had armed themselves with the newest industrial weapons. 

  • For centuries the British had maintained Europe’s largest naval fleet, which was necessary for both an island nation and the world’s largest colonizer country.
  • At the start of the 20th century, Germany embarked on a massive naval buildup by investing in many battleships and submarines. Germany also heavily invested in munitions. As the German military budget increased, other European nations increased their production. 

The spark that lit the fire: the assassination

Slavic nationalism in the Balkans was a significant factor  in the start of WWI as Pan-Slavic groups fought for the Slavic people to have a Slavic nation.

  • When Austria-Hungary annexed (added to Austria-Hungry) Bosnia and Herzegovina (home to many Slavs) in Eastern Europe, Slavic nationalist groups expanded.
  • One such group was named the Black Hand and had the stated goal of removing Austria-Hungary’s influence in the region.
  • On June 28, 1915, Gavrilo Princip, a member of the Black Hand, assassinated the heir to the Austrian imperial throne Archduke Franz Ferdinand and his wife while they were on a trip to Sarajevo, Bosnia.
  • In response, Austria-Hungary invaded Serbia, activating the Serbian alliance with Russia. Russia then declared war on Austria-Hungary. The rest of the alliance system kicked in, and Europe was at war.