The precise statement is, "To conquer a nation first replace science with Christianity."
We have rated this quote Misattributed, because there is no evidence the Nazi dictator ever said such a thing, or anything resembling it. Although Nazi Germany boasted some topnotch scientists, some of whose talents were recruited by the military for the war effort, Hitler reportedly showed little personal interest in, and even less working knowledge of, the sciences.
It's relevant to note, as well, that Hitler is known to have made at least one very positive statement about Christianity, "We tolerate no one in our ranks who attacks the ideas of Christianity. Our movement is Christian." There is little reason to conclude that he meant those words, however, given that Hitler's regime persecuted Christians who refused to toe the Nazi line.
In any case, we found no published instances of the statement about replacing science with Christianity predating 2015, when it first surfaced on the internet, yet another indication that it is apocryphal. Snopes previously fact-checked another alleged Hitler quote that begins with the identical phrase: "To conquer a nation, you must first disarm its citizens." We determined it was not an exact quote, though it can be described as a rough paraphrase of a lengthier statement he did make.
The present example, "To conquer a nation, first replace science with Christianity," is nowhere to be found in published literature and appears to be a fabricated variant of the "disarm its citizens" quote.