I looked that up, Madam.
Why were they hanged? Intruding on someone else's territory in the labor market, or something?
No, they were were 3 black men and they were just traveling through with a circus at the time. Accused of raping a white gal.
They were not all guilty, though. Around here, it's told one did it but all three were hanged. Hard to know, though, if any of them were guilty.
There are pics at the link, but I sure didn't want to post them.
Here's a start page. http://collections.mnhs.org/duluthlynchings/html/lynchings.htm