When World War l broke out in 1914, one of the reasons was actually the extreme feeling of patriotism, or nationalism, that citizens had toward their respective European countries. For example, various ethnic groups who felt loyal to their homelands like the Czech and Poles resented being dominated by other countries who wanted control of their land. Also, countries like Austria, France, Germany, and Russia who were concerned about their own national interests, wanted control over Serbia. So, ultimately one of the reasons WWl was started was because countries were only thinking about themselves and what was good for their country instead of what was good for the entirety of Europe.
