No, it is the Grace of God restraining evil. We won't know how much until we get to heaven, but I believe, when the panoply of history, is revealed, all mouths will be stopped and all will be shocked by the extent of God's Grace in preventing some tragedies and allowing others.
Ask not, why God allowed it, but why he is patient with mankind at all. For he owes nothing to man, and he can do as he wills.
Mass murder was prevented in the 1993 WTC bombing when the poison gas that the terrorists used was incinerated by their bomb. Imagine if people had died trying to exit the stairwells.