What example of militarism told europeans that the region was on the edge of war?

The correct answer is Germany stockpiled an enormous number of modern weapons

Although Germany was forbidden from making weapons after world war 1, they eventually started making it and modernizing their military. This was a warning for others because a country doesn't prepare for war unless it actually plans to fight in one so it raised a red flag and showed everyone that they also needed to develop their military more.