How about the Norman invasion of Britain? Or the Roman occupation of Britain, for that matter? There are plenty of examples (Alexander the Great) where invasion did not result in implacable resistance. How about the Allied invasion of the European continent at D-Day? American occupation of Japan? Union invasion of the Confederacy?
Invasion is like going to court. Anything can happen and justice has nothing to do with it.
On the other issue, I wonder if Italy could be considered an ally of Germany at all?
Militarily, they were thoroughly incompetent and just too decent a people to be any help for the Nazi cause. Italians saved many more Jews in their society than the French did! The vast majority of Italians just refused to participate in the Jewish extermination programs and actively shielded Italian Jews from persecution. Italians were tempermentally unsuited for the dark side.
I think Hitler was not helping Italy, but doing the opposite: attempting to dominate a reluctant but grandiose misfit. In effect he was occupying an ally!