The most important cause of World War I in Europe from the four main causes was Nationalism.
There were four main causes for the outbreak of the first World War and they included militarism, alliances, nationalism, and imperialism. Arguably, the most important in causing World War I to break out was nationalism as it was the one that sparked the war. It was because of nationalism that a very important figure was killed which then set in motion a series of declarations of war that led to the First World War.
The important figure that was killed, or rather assassinated, was Archduke Franz Ferdinand who was the heir to the imperial throne of the Austria - Hungary empire. As a result, the empire demanded blood and turned their wrath on Serbia which was allied with Russia which was allied with France and Britain. Germany was allied with the Austrians and so the first World War broke out.
Find out more on the causes of WWI at https://brainly.com/question/27037534
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