Was the machine gun effective in World War 1?

The Machine gun was the most effective weapon in world war one. It killed more than 7million people out of 8 1/2million. Used to protect trenches. It was effective enough that a counter measure had to be developed to overcome it. The tank. Even in WW2, Gen Patton stated that the primary weapon of a tank was it's machine gun, and not it's cannon.
Was and still is.