Oh, a historian’s parlor game! So many possible answers. However, I’d add this one:
Thomas Newcomen’s invention, in 1712, of the first commercially successful steam engine. This was one of the earliest inventions in what we now know as the Industrial Revolution, a revolution that irrevocably changed our global history both for better and for worse. We have benefited from it in many ways (the invention of items such as washing machines, vaccuum cleaners, and other household contraptions radically changed women’s roles, for one thing), and suffered from it in others (the pollution that emanated from these inventions is contributing to our current climate woes, the repercussions of which could be terrifying and unimaginable). We have never been the same since.