Darwinism was the first real, damaging stab at God in the modern era. It was one thing to attribute geology to plate tectonics or plants & trees to cells - but it was quite another to fully explain the diversity of life, which had often been invoked as proof of God's glory, as being a logical procession of organisms responding to their environment. This was truly blasphemy, and Charles Darwin, who had considered joining the clergy in his youth, knew it. Of course, Darwinism was not a clean cut through God; some of the gristle remained attached by its inability to explain what might have started the cellular pageant. But God's involvement, if any, had ended several billion years ago, somewhat reviving the hopes of Deists (God-as-Watchmaker). Unfortunately the Deist Church has trouble justifying its own existence and so did not flourish.
Darwinism was adopted early on by large colonial powers. It was a way of assuaging their nagging guilt over the torture, murder and slavery of virtually the entire continents of North America, South America, Australia and Africa. "We are able to subjugate countless million savages", thinks the Imperial mind, "therefore it is only natural and scientific that we continue to do so". Imagine the ripple effect an idea like this would have as it spread throughout Europe. Any person who wished to persecute or kill would suddenly have ample justification, and worse make them more committed to their cause. Eliminating scientifically-proven inferior races and cultures became a sort of White Man's Burden in his flawless pursuit of scientific ideal.
It's no surprise that it took two Globe-spanning wars of unimaginably violent nature to close out Imperialist Darwinism for good - flawless justification for savage acts is a hard thing to abandon. As a result, most Post-WWII dictatorships took the "Our people love me, why else would I win twelve consecutive elections" route of self-deception. Or for Communist countries, "We are not a party; we are the government, and the people nominate and elect who they wish free of partisan thinking". Fidel Castro in particular goes this route. Ironically, this turns communist party hierarchies into institutions very closely resembling corporations, where upward mobility depends on proven loyalty; and making it to the top means being the consummate "company man" and having a healthy taste for treachery.
The Scientific Revolution gave people the ability to be atheists by giving them proof, in a sense, that what is around them is not God's creation. Before, it was a risky crapshoot; renouncing God was a dicey proposition in ye olde Village, and no-one could have any certainty whatsoever that the World was not just some omnipotent whim. "Well why is the sky blue?" a Medieval learned man would ask a skeptic. "I don't know either; nobody knows. That's because it's God's creation." Done, ipso facto. Said skeptic would also be burned alive for good measure; a "wholesome physick" for apostasy.
Nowadays, the burden of proof is reversed; Organized Religion had better produce some scientific basis soon, otherwise it is doomed. Not everywhere, of course; 11th century Islam had far more scientific curiosity than it does now, but that's what happens when you believe your holy book is, literally, the words of God as spoken directly. It seems to make significant religious amendment or modification difficult, leaving orthodoxer-than-thou interpretation the only means for someone to become an authority. Any beautiful defense of a tract of elegantly written criticisms could be quickly dismissed with a sarcastic comment from the Imam such as "great, well you know what, God wrote the Koran. Who the fuck are you? End of discussion." And, like a Catholic atoning with hail marys, the Imam might crunch the numbers and conclude that 1 violent death, 4 rapes (immediate family) and twelve (12) beatings would constitute the necessary atonement for blasphemy. *sigh* God's will be done.