It is not really about skin color or cultural heritage but about class. The skin color happened to be the manifestation and the marker of class divisions in the US. It is not that there are inequalities because there are racial divisions in the US, but the other way around - racial divisions are created by class divisions. If there were no blacks in the US, the class divisions would still be there, only manifested differently, perhaps by ethnicity (Eastern European? Mediterranean? Asian? Latino?) perhaps by residence (North vs South? Urban vs rural?) perhaps by look (slim vs obese, blonde vs dark or perhaps having the "wrong" shape of the nose), or perhaps simply by possession.
Wojtek
^^^^ CB: For the U.S. Left, perhaps a good historical point to mark clarifications of different positions on this issue is the origin of the Communist Party in a split from the Socialist Party in 1919. The Socialist Party, Debs, et al. had a position similar to what you articulate here. The CP took a position that Black workers in the U.S. suffer special racist oppression in addition to oppression as workers, and that working class partisans in the U.S. ( especially white radicals) must participate in specific struggles aimed especially against racism.
For example, a more current discussion
www.pww.org/archives95/95-12-09-2.html