Amish men shave their mustaches as a protest against violence. The Amish were originally founded in Europe. At the time, mustaches were prevalent in the German military. The Amish began shaving their mustaches as a physical representation of their non-violent nature. It continues today.
Hitler originally had a handlebar mustache, but was ordered to shave it to his famous toothbrush style during WWI in order for his gas mask to fit air tight.
From the late 19th century to 1916, mustaches were mandatory in the British Army. Soldiers were forbidden to shave their upper lip.