I agree with Blashy,
If I had my way, nothing except the concept and the beginning of the game would have anything to do with what really happened during WW2.
Meaning that when you start a scenario everything is historicaly correct(except if you have edited it with the editor) but from that moment on I can declare war, make peace, move troops,sack commanders,promote commanders,retreat,attack,... in short everything I want to do(excuse me if I sound a bit dicatorish).
BUT(another but) I would also have to take the responsibilities for my actions.
e.g.: if I let the Fins be slaughtered after they joined me, a lot of countries would be less inclined to join the axis like they have.
the same for the allies, if I were to order the full evacuation of , say Yugoslavia, right after they joined me(I don't know how I would do that since they have no port,but anyway..),
A lot of minors would think that the English are only interested in them for the troops they can provide and not in their economy or people.
As for countries that are declared war on by the axis, it would simply make no sense for the allies to emmediately evacuate because then it would be a total victory for the germans without even a loss of material.