Indeed, some discoveries created the power to destroy humanity itself. ‘Indeed’ is a word that Americans would use to sound stereotypically British. We’d more likely use actually or certainly.

You can use 'indeed' but in a different order. "Some discoveries indeed brought the power to destroy humanity itself. However, it does sound a little archaic and something Great Granny used to say, as well as being very, very formal.

Hi Ana Indeed is defined as a word used to emphasize the truth of something, to agree that something is true, used in an affirmative comment or to express surprise, skepticism, or irony. So if your sentence has a sarcastic tone, yes, indeed is good there otherwise I'd say: "Some discoveries (certainly; truly; actually) brought the power to destroy humanity itself"

Hi Ana Indeed is defined as a word used to emphasize the truth of something, to agree that something is true, used in an affirmative comment or to express surprise, skepticism, or irony. So if your sentence has a sarcastic tone, yes, indeed is good there otherwise I'd say: "Some discoveries (certainly; truly; actually) brought the power to destroy humanity itself"