an excellent point.
But would God really simply sit there and watch as millions of helpless people died? I mean, it wasn't the prisoners' faults!
Also, if God knew the Allies would win, that would mean that there is destiny. If there is destiny, we'll never have time travel, or someone would have shown up by now
I don't think God could know what is going to happen, as that is the unknowable. Even if He does, at some point he must not have known.
Of course there's the argument that God lives outside the universe, but then, prayer wouldn't "reach" him correctly... if he has already experienced the future, he cannot change the past without changing its future, perhaps killing future people with a prayer He answers.