What was the most important cause of the First World War?

The overall cause of World War was the assassination of Archduke Franz Ferdinand. Nationalism was a great cause of World War one because of countries being greedy and not negotiating. Nationalism shows you are proud of your country and want it to be the best.

Explanation:

The Crusades

Explanation:

The Crusades were a series of religious wars that took place in western Asia and Europe and that were encouraged by the Catholic Church. Their main purpose was to "recover" the Holy Land that was controlled by the Muslims. These wars took place between the 11th and the 17th century, and left a lasting mark in Western culture. Although considered a military failure, the Crusades helped stimulate trade during the Romanesque period.