Final answer:
The most direct cause of the war happening was the assassination of the Austrian Archduke Franz Ferdinand in 1914.
Step-by-step explanation:
The most direct cause of the war happening was the assassination of the Austrian Archduke Franz Ferdinand in 1914. This event ignited the conflict and led to the outbreak of World War I. Franz Ferdinand's assassination was carried out by a young Serbian nationalist and it directly contributed to the war starting.