I don't think killing a million Irish will help.
Trying to end the conflict by an attempt to kill to the last man didn't work for the Germans in WWII, the Soviets in Afghanistan or the US in Vietnam for that matter.
Firepower alone cannot win a terrorist war.
I by no means believe that there are a million Irish who can be called terrorists in this sense.
The war in Europe was a war of conquest. Hitler's "final solution" was not aimed at a terrorist organization, it was aimed at peaceful Jews and Poles etc.
Our effort in VietNam failed precisely because we did NOT pursue the war in this manner. We constantly let the enemy withdraw, regroup and return, instead of inflicting the total devastation we were capable of.