If I had a nickel for every time somebody tried to tell me that De Beers "invented" the concept of diamond engagement rings, I could probably buy a really nice diamond engagement ring!
De Beers of course massively contributed to the ubiquity of the diamond as an engagement gift in the twentieth century, but in reality diamond rings have been considered a traditional betrothal gift long before copywriter Frances Gerety penned the phrase 'a diamond is forever' in 1947.
Luckily, while flipping through super old issues of House & Garden magazine (the March 1928 issue, to be exact), I stumbled across this advertisement by Black, Starr & Frost:
Here it is in black and white, proof that diamond solitaire engagement rings were an established American tradition decades earlier than De Beers' famed campaign.