Basically, the primary factions of Middle Earth during the third age against the armies of Westeros. (This may or may not have been a thing before but what the hell).
Lol, Sauron has millions under his thralldom, this is a stomp for the people of Middle-earth. That isn't even mentioning the political advantages of the forces of Middle-earth.
Edit: However how badly you want to see Westeros screwed depends on which point in time during the 3rd Age.
2nd Edit: About the only time period Westeros stands a chance is the time period after the Great Plague.
Hobit, Chief of the Inquisition(Inform me of heretics)
What do you think?