Well, according to Herodotus (who wrote what's generally considered to be the first history), it includes a study of cause and effect. Is there value in looking at the past via data that wasn't considered by previous historians? Ask the students during pre-Civil Rights South, when they were commonly taught about the War of Northern Aggression. Ask the students during the Communist era in the Soviet Union. Ask the students in North Korea (I have no idea what they study, but I'm sure it's a pretty single-focus view).
There is always value in looking at history through different lenses, particularly as the study of history reveals power structures that might have colored what was recorded. That calls into doubt the completeness of the record.
Even if you disagree with the premise, even if you think that slavery is a normal part of human social evolution, even if you think that the US was really founded by the Pilgrims, and that the stage wasn't set by all the Spaniards and others who came earlier, spreading horses and disease among other things, there's value in studying all that other stuff.
Wendy P.