Causes of WWI The overall cause of WWI in Europe during the1800’s and 1900’s was the large amount of people who agreed with nationalism. Nationalism is patriotic feelings, principles, or efforts. Almost everyone during this time was involved in the war and very patriotic about their country. Most European countries had their own motives that built up to WWI which affected many surrounding countries as well. Almost all countries were very prepared for this war because militarism also played a great role in the rise to WWI. So overall nationalism and militarism were the biggest factors of the build up of WWI. To go more in depth Nationalism is defined as “excessive patriotism;the desire for national advancement and devotion and loyalty to one's