This is an interesting question, but I believe I have a solution.
Player 1 - England
Player 2 - Australia
Player 3 - India
Player 4 - Canada
Player 5 - Egypt
Player 6 - New Zealand
Player 7 - Scotland
Player 8 - South Africa
Player 9 - Germany, Japan, France, USSR, Italy, US, China
This is optimal set up for a nine player game. We should divide up the British Empire, since they are way too powerful. World War 2 was mostly about breaking up the British Empire, so it would make sense to break it up between players to show the arguing within the empire, while the other powers, controlled by only one player since they are unimportant, fight each other.