My favorite response to anyone's question about how something happened.
Really, Mom, I was just sittin' here mindin' my own business!
Every casualty suffered by an invader to Afghanistan boosts recruitment of the insurgent side.
In a like manner, every casualty suffered against zombies recruits more zombies.
A never-ending supply of recruits for the opposing side is a stalemate at best.
And with this comment the thread is pretty much complete...