I just don't get this. How in the name of fluffy cute bunnies can you arrive at "White Supremacy" never played a factor against minorities in the United States? Have you never opened a history book, or watched a movie about the past, or spoken with grandparents? Conspiracy mongering aside, nobody denies slavery was a thing. There wasn't some level of compensation upon release, there were well documented groups murdering and harassing folks trying to work hard and make a better life, and there is a clear line of when laws came into being that kinda doesn't make sense if emancipation just cured racial inequality.
The answer is discrimination by race in law has been illegal for more than 50 years. Don't put words in my mouth, obviously white supremacy and systemic racism have played a major roll in the oppression of african americans, but we've progressed past that on a governmental level you cannot find a law in the books that discriminates based on race
Things have not progressed that far since, and economic mobility in the United States isn't nearly as great as you seem to make it out to be. Poor people tend to remain poor, even if they have skill and enthusiasm, because it often takes money to make money. Social programs are supposed to exist to allow everyone stuck at what we collectively would call the bottom of society to start moving upward, but every state has their own race to the bottom that makes moving while poor unrealistic, and stuck with a myriad of hoops and catches that makes it outright likely to end in failure, which is a thing that lets the poor go into even further problems. As such, there is no bottom, save being on the streets in the cold.
It's true many African Americans are in impoverished neighborhoods and may struggle to get out of said hardship, but this all comes down to a cultural issue that creates a cycle of poverty, it's not a systemic issue revolving around one's pigmentation in our laws. Proof: Nigerian Americans, people that are just as black as african americans are some of the most successful races in our country. We've tried a welfare system and that hardly helped in the slightest to help African American break out of a spiral of poverty, there needs to be people within the community that break the spiral (And that means emphasizing the value of hardwork, Monogamy and staying in a healthy relationship, etc etc).
Marxism is never the answer to these problems. The solution to helping races isn't to oppress everyone else, trust me.