Christianity.
But you've just pointed out that Christianity was 'checked', so how come it is still around? In fact, was it ever checked, in the 'halted' sense?
Alas, no
Although in recent human history it's dying out in the developed world, thank goodness.
Argumentum ad particular populum.
No. It would have been the
argumentum ad populum if I'd tried to make a case that Christianity is untrue
because adherence to it is dying out in the developed world - it's the
because bit that makes the fallacy. That would have been a fallacious argument; Hope has already accused me of emplying the logical fallacy of negative proof/argument from-appeal to ignorance and I've asked him for evidence of where and when I have done this. So far, no dice.
(Alan Burns provided an absolutely gob-smackingly classic example of this specific fallacy not long ago*, but of course we're not going to expect Hope to raise this with him).
As it is, all I stated was simply a matter of demonstrable fact (and my opinion about that fact).
ETA: As Lenny has just also pointed out. Hola, Len!
*
http://goo.gl/b3si1l