How was mititarism a cause of world war l?

Militarism is "the belief or desire of a government or people that a country should maintain a strong military capability and be prepared to use it aggressively to defend or promote national interests."

It was widespread prior to World War I and it, in combination with a network of treaties, let the world down the violent road of World War I as nations were heavily armed, belligerent, and ready to fight.