How did militarism play a role in sparking World War I? Each of the major powers considered itself superior to the others. Each of the major powers considered its military strength superior to others. All of the major powers considered war to be part of a valid foreign policy. All major powers believed they could threaten war and none would call their bluff.
"All of the major powers considered war to be part of a valid foreign policy" is the best option, but it should be noted that militarism was a consequence of nationalism.
