I've put together a co-existing setting that takes place in Los Angeles (the game clearly states that other cities around the world have also been attacked). I played a quick game in the world using Evil Bear Games OSC.
Turn 1, scavengers deployment point
Turn 2, Scavengers get into camp
Turn 1, California National Guard deployment
Turn 2, CNG squad takes cover and opens fire
Turn 2 end, Grenade hits police car and wipes out most Scavengers
Turn 3, CNG soldier gets behind but jams
End game, TPK for Scavengers