How did intense nationalism lead to the First World War?

An important cause of the war was intense nationalism or "competitive patriotism".

1. Germany had Kaiser Wilhelm II as her new Emperor.
2. He went about proclaiming that "Germany was going to be the leader of the world."
3. He wanted to establish a vast German Empire and gain important position in the international sphere.
4. France and Germany were old rivals.
5. After defeating France in the Franco-Prussian War (1870-71) Germany had seized the province of Alsace and most parts of Lorraine, which were rich in minerals and industrial products.
6. The French dreamed of revenge and of taking back their lost provinces.
7. The Italians desired to get back Trentino and the Port of Trieste which were inhabited by Italians but were still the part of Austria-Hungary.
8. Then there was the "unsatisfied national spirit of the Balkan States—Serbia and Bulgaria, of Poland and of the people of Austria-Hungary."
9. The political leaders were successful in fanning hatred and passion under the cover of nationalism.