In 1781, which James invented the steam engine?

Steam engines already existed. Watt improved the efficiency by use of a condenser.

Somehow if you are observant you can improve and invent things

konablacktraveler, Watt invented a good steam engine; Fulton had improvements incorporated for his steamboat invention.

way back when, we were taught it was a guy named Robert Fulton, but that was when Pluto was still a planet! 😆

So he didn't invent it but improved it