Historically, the labor movement has seen a lack of solidarity between poor white and black workers due to the exploitation of black workers for cheap labor. In the case of the 1892 Homestead Strike, only a small number of workers belonged to the union before the strike, but the majority of workers joined once the factory closed.
During the Homestead strike of 1892, 3000 workers occupied the plant and took over the town of Homestead for the first time in American history. The strike was met with a failed aquatic landing attempt by the Pinkertons and ultimately led to the destruction of the union.
The Pinkerton's attempted to land in Homestead, but when they ignored the warning given to them, the homesteaders started shooting at them, and a gun battle raged on for 12 hours. The homesteaders had limited weapons, but they managed to fight off the Pinkertons using a 20-pound cannon and dynamites as grenades.
The Great Railroad Strike of 1877 saw violent clashes between workers and authorities as railroad workers went on strike to protest against wage cuts. The strike, which lasted for 45 days, was finally suppressed by a combination of federal troops and militias.
The lack of solidarity between poor black and poor white people has an obvious reason - the history of poor white people oppressing black people. The government, serving the interests of wealthy mine owners, suppressed the strike of poor workers, both black and white.
The Homestead Strike ended in victory for the union and the town, but it was not without its consequences. The Pinkertons were never the same agency following their involvement and the aftermath of the strike solidified unionization in Homestead for over 30 years.