There were many factors that led to the start of World War I. One of them was nationalism. A wave of nationalism was sweeping through Europe in the early 1900s. Countries began to believe they were better than any other country. They believed they could do whatever they wanted, and they could beat any country in a war if that country tried to stop them from achieving their goals.
Another cause was imperialism. Germany got into the colonizing mode very late. By the time Germany was unified, almost all lands available for colonization were already gone. The only way Germany could get colonies was to attack countries that had them.
A third reason why World War I began was militarism. Countries began to build up their military strength. Usually when a country increases their military, they usually have plans to use it. As Germany built up its military, so did the other Allied countries.
Entangling alliances were another cause of the war. When countries formed these alliances, it created the possibility that a war between two countries could quickly escalate into a multi-nation war. When Austria-Hungary declared war on Serbia, it led to a chain reaction where members of the Triple Alliance and members of the Triple Entente declared war on each other.
The event that sparked the start of World War I was the assassination of Franz Ferdinand. Franz Ferdinand was supposed to be the next King of Austria-Hungary. When a group of Serbian nationals assassinated Franz Ferdinand, Austria-Hungary made a series of demands on Serbia. When Serbia couldn’t meet all of these demands, Austria-Hungary declared war on Serbia. Russia then declared war on Austria-Hungary. This started the chain reaction of alliance members joining the war as one member of the Triple Alliance and one member of the Triple Entente declared war on each other.
Many factors led to the start of World War I. Most causes had been simmering for years while one cause was the spark that ignited the war.