Many races has been submitted to slavery in the United States.

You'll have to elaborate on this. While other races certainly experiences hostility and outright racism, no other race of people even comes close to the institutionalized slavery experienced by African Americans. Some races, such as Southern and Eastern Europeans, experienced institutionalized racism such as the Immigration Act of 1924 or the Emergency Quota Act but again, nothing comes close to what Africans experienced (with the possible exception of Native Americans).

Also, it's worth noting that this institutionalized racism ended in the 1960's (and by institutional racism I mean actual laws set in place to disenfranchise African Americans). This really isn't ancient history for the United States seeing as the generation that experienced the Civil Rights movement is still alive. I'm not African American so I can't speak as to "why African Americans are the only ones vocal about it" (which, by the way, I thoroughly disagree with) so I can only say that we are a generation removed from an era that saw one of the most disproportionately discriminated groups of American citizens finally receive the rights already enjoyed by their white counterparts. I really feel as though you're overlooking just how recent the Civil Rights era was and how hard African Americans had to fight to earn those rights.

On a side note, some historians have suggested that the seeds for the Civil Rights era were planted during WWII as some Americans began to wonder what the difference was between businesses refusing service to Jews in Nazi Germany and businesses refusing service to blacks in Tallahassee, Florida.