World War 1 was caused by a number of issues, like leader's aggression towards other countries. This was backed by the rising nationalism of the European countries. Economic and imperial power, fear of war urged military alliances and arms race. This would further increase the tension contributing to the outbreak of war. The continent of Europe spilt into two conflicting sides, so many different powers were siding in mutual defense agreements, when the war did happen, it involved nearly every country in Europe. When alliances were signed, some countries were forced to support policies implemented by their partners, which was not taken so easily. .
In some ways the basic causes of World War 1 goes back as far as the early 1800's. People controlled by other countries began to develop feelings of nationalism and patriotisms, often referred to as consciousness of sharing a common past and a closeness of speaking the same language. For Twenty years, the nations in Europe had been making alliances, they thought it would promote peace and that others would be protected by each country in case of war, making it foolish for one country to declare war on another. The danger of these alliances was that an argument between two countries could draw all the other nations into a fight. This is just what happened when a conflict between Austria-Hungary and Serbia led to World War 1. So countries started to group together in rival of military alliances to advance their aims. .
Quite similar to the arms race of today, because Britain had a great navy, Germany wanted a great navy too. Germany and France competed for larger armies. The more one nation built up its army and navy, the more other nations felt they had to do the same. Thus enhancing the power of industrial development and so forth.
The competition for colonies was another source of national power and strength. The great powers of Europe sectioned off Africa among them establishing a solid influence in China.
