Mutual defense agreements are what caused a small conflict to turn into WWI.  


Over time, countries throughout Europe made mutual defense agreements that would pull them into battle. If one country was attacked, allied countries were forced to defend them. Before World War 1, the following alliances existed:

  • Russia and Serbia
  • Germany and Austria-Hungary
  • France and Russia
  • Britain and France and Belgium
  • Japan and Britain

After the assassination of Archduke Ferdinand, Austria-Hungary declared war on Serbia. Russia got involved to defend Serbia. Germany, seeing Russia mobilizing, declared war on Russia. France was then drawn in against Germany and Austria-Hungary. Germany attacked France through Belgium pulling Britain into war. Then Japan entered the war. Later, Italy and the United States entered on the side of the allies.

Although mutual defense alliances are the main cause of WWI, there are a few other reasons influencing world war.



Imperialism is when a country increases their power and wealth by taking additional territories under their control. Before World War 1, Africa and parts of Asia were highly coveted and fought over by the European countries. They were of such contest because of the raw materials these areas could provide. The increasing competition and desire for greater empires led to an increase in conflict, which helped push the world into World War I.


As the world entered the 20th century, an arms race had begun. By 1914, Germany had the greatest increase in military buildup. Great Britain and Germany both greatly increased their navies in this time period. In Germany and Russia and other countries involved, the military buildup began to have a greater influence on public policy. This increase in militarism gave the need for war a greater push.


Many Slavic peoples in Bosnia and Herzegovina no longer wanted to be part of Austria Hungary, but instead be part of Serbia. In this way, nationalism led directly to the War. The nationalism of the various countries throughout Europe contributed to both the beginning and the extension of the war in Europe.

The immediate cause of World War I that made all the other causes of war that I mentioned was the assassination of Archduke Franz Ferdinand of Austria-Hungary. In June 1914, a Serbian nationalist assassinated Ferdinand and his wife while they were in Bosnia which was part of Austria-Hungary. The assassination was in protest to Austria-Hungary having control of this region. Serbia wanted to take over Bosnia and Herzegovina. The assassination led to Austria-Hungary declaring war on Serbia. When Russia began to mobilize due to its alliance with Serbia, Germany declared war on Russia. Thus began the expansion of the war to include all those involved in the mutual defense alliances, and WWI began.


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