What does “black men” mean here?

Question

Uncle Al and August scour Billboard and at each stop make telephone calls and send telegrams in an effort to recruit a new one, but all known fat ladies appear either to be happy in their current situation or else leery of Uncle Al's reputation. After two weeks and ten jumps, Uncle Al is so desperate he approaches a woman of generous proportions in the audience. Unfortunately, she turns out to be Mrs. Police Superintendent, and Uncle Al ends up with a shiny purple eye instead of a fat lady, along with summary instructions to leave town.
   We have two hours. The performers immediately sequester themselves in their train cars. The roustabouts, once roused, run around like headless chickens. Uncle Al is breathless and purple, waving his cane and whacking people if they're not moving fast enough for his liking. Tents drop so quickly that men get trapped inside, and then men who are dropping other tents must come and retrieve them before they suffocate in a vast expanse of canvas, or-worse, in Uncle Al's estimation-use their pocketknives to cut a breathing hole.
   After all the stock is loaded I retire to the ring stock car. I don't like the look of the townsmen hovering around the edge of the lot. Many are armed, and a bad feeling ferments in the pit of my stomach. I haven't seen Walter yet, and I pace back and forth in front of the open door, scanning the lot. The black men have long since hidden themselves aboard the Flying Squadron, and I'm not at all convinced that the mob won't content themselves with a redheaded dwarf instead. (Sara Gruen, Water for Elephants)

I don’t understand what black men means in the context. For there was no comment at all about black working men before. So I’m supposing if they might be the blamed guys, yet Al alone has approached the woman for recruiting a fat lady performer. What does black men mean?

Answer 1

The black men are just that: African American workers in the circus.

Water for Elephants is set in the Depression era—the 1930s—at a time when mob violence was just beginning to decline in the United States. It would be only natural for African Americans in the circus to hide when violence threatened: most of the victims of “lynch law” were African Americans, and they would be the first targets of angry townsmen, since in practice there was little likelihood that violence against African Americans would be punished.

This 1939 picture (check FumbleFingers' comment below before you look at it) and the song it inspired ("Strange Fruit") capture the terrible danger which the black men faced.