The theory that the moon landings were hoaxed by the US government to assert their victory in the space race over Russia, is something which has grown in popularity over time.

Recent polls indicate that approximately 20% of Americans believe that the U.S. has never landed on the moon. After the Apollo missions ended in the seventies, why haven’t we ever been back? Only during the term of Richard Nixon did humanity ever land on the moon, and after Watergate most people wouldn’t put it past Tricky Dick to fake them to put America in good standing in the Cold War.

I can't understand why 'did' is written before the noun 'humanity'. I know that we sometimes use 'did' in a sentence that is not a question, as in "I did study Chemistry! ", to emphasize the verb, but why is it use that way in this article?

Your explanation is really appreciated. Thanks for the help!