Having the will and means to defend oneself is not the same thing as a genetic change that enables one to survive better on available resources. Infants are born with the ability to produce an enzyme called lactase which enables them to metabolize the lactose (sugar) in their mother’s milk. As they get older they lose the capacity to produce lactase enzyme and can no longer consume milk without digestive problems.
However, a new mutation occurred in someone which enabled them to produce lactase into adulthood. Thus they could consume nutritious milk that others could not. Their children when inheriting this gene also had a survival advantage and passed the gene on to additional offspring. Eventually there was a large enough group to go migrating into Europe where their ability to drink milk year round gave them a survival advantage. Whether warfare was involved is a separate matter. I am talking biology, not behavior.
Your “new mutation” example is somewhat flawed; that the babies of both groups produce lactase means that the [genetic] information to do so was present in both groups. Further how do you know that the Europeans weren’t the ‘mutants’ with the common genetic defect of their lactase production?
HGH is an example of something that, in the normal population, dies-off in production after a certain age. Some people have defective “off switches” for their HGH production and so always produce it; a famous person with that condition would be Andre the Giant (The Princess Bride, The Incredible Hulk).
But in both these cases, your lactase example & my HGH example, both groups are STILL human.