@aequitas:
The Allied Player attacked Portugal and Spain on his turn as the US and flew planes over Spain to Yugoslavia.
Doing so implies a sort of order in combat movements, such as:
First combat movement: Attack Spain so Spain is no longer neutral.
afterwards:
Second combat movement: Fly over Spain to attack Yugoslavia.
As written above “All combat movement is considered to take place at the same time.” (Rulebook Europe, page 13).
So the implied order is not possible.
At the start of the combat movement phase and before all combat moves Spain is neutral. Now all combat moves occur simultaneously.
And Spain losing its neutrality is a consequence of a combat move.