Before 1914 the five Great Powers, Great Britain, France, Germany, Austria-Hungary and Russia controlled Europe. In 1914 World War One broke out in Europe. Historians have debated the causes ever since. As a historian it will be difficult to conclusively establish a single cause a number of significant causes is a far more helpful outcome. Although the European Alliances were certainly a cause of WWI, there were many other causes as well. Along with the European Alliances there was Nationalism, Imperialism, Militarism, and of course the physical conflicts leading up to the war. All these issues blew up the balloon of tension, which just needed a tiny pinprick to burst into war.
The European Alliances had a major part in beginning WWI. After the build up of tension from Nationalism, Imperialism and Militarism, the Powers were worried about being attacked by each other. To counter this alliances were formed. Germany made a secret alliance with Austria-Hungary in 1879. Three years later Italy joined this Dual Alliance to form the Triple Alliance because it was annoyed with France for stopping its plans to colonise North Africa. The rest of the Great Powers became increasingly worried about the strength of the Triple Alliance. Believing they could be defeated by Germany, Austria and Italy acting together. France and Russia agreed to help each other if attacked. Britain was worried because it had no allies among the Powers, but it was not prepared to ally with Germany after the Boer War. In 1904 France and Britain were prepared to forget their previous quarrels and enter an agreement. Finally in 1907 France brought all three nations together to form the Triple Entente. The Alliance System was definitely a prominent cause of WWI. If Germany hadn't allied with Austria the war might've been averted. For example if a conflict occurred just between Germany and Great Britain the rest of Europe would not be pulled into it. World War One spread because of the Alliance system, even with the tension build up it would've still been just another European war.
Nationalism was the next major long-term cause of WWI. Nationalism involved all those who shared a common language, history and culture. It was a strong feeling of support for one's own nation. Nationalists believed that the needs of their nation were more important than the needs of other nations. Nationalists were so proud of their nation that they wanted it to be the richest and most important and recognised as such. Such strong feelings made the countries very aggressive towards other nations and quite unforgiving if their nation had been offended. It was nationalism that encouraged Givrilo Princip to shoot dead the Austrian heir. Nationalism greatly blew up the tension and had an influence in causing WWI.
Imperialism was another long-term cause of tension among the Powers, which led to war. Imperialism is the desire of nations to own colonies and form an empire. European countries had been taking over colonies throughout the world since the fifteenth century. From 1870 on there was an unwritten competition to take over parts of the world they had earlier considered not worth colonising. Britain and France, and Germany and France had almost gone to war over clashes in North Africa. Italy resented France because they prevented the setting up of Italian colonies, and the British and Russians clashed over who should have control in Persia (modern Iran), but were both worried that Germany would take land in the Middle East. Imperialism had an important side effect that explains why the Great War' became a world war. As each European country gained colonies, those colonies became committed to helping the motherland' in the event of a war.
The last long-term cause of WWI is Militarism. Militarism also built up...