Yes!! In fact one player could play both Entente factions and the Central Powers.
So how you do this is up to you, but if there are two players, you can do the shared hosting many players enjoy. One player starts the game, say you do this. You create the game, make your move, and save. Then you send all files to your opponent in a zip, rar or through dropbox. You Entente opponent does this:
Plays one side, say Western Entente, and saves. Exits the game. Then enters as the other faction, Eastern Entente. Makes the Eastern move and saves. Then executes the turn.
Next he makes both the Eastern and Western moves, saving each when completed and sends all files to you.