[AlexW]

“Negro, simply meaning black in Spanish, had to be discarded by those of Jackson’s ilk because it was used during the slave era. It wasn’t the only name used then for blacks, but it was the most polite.”
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Actually “Colored” was the most polite, but back when I was in grade school, the three prominent races were: Caucasian, Negroid, and Mongoloid.
Every area of the world, including the US, had their own derivations. My grandmother in Atlanta used the term “Nigra”, and it was not in a derogatory way.
Some, but not all, were considered degrading.

[luvbach1]

Not to dispute what you said, but if colored was the most polite I don't know why negro was used quite often in the names of black organizations. Also, as a young boy I visited segregated parts of Oklahoma in 1943 and remember seeing fountains with the signs reading: WHITE and COLORED in the train station. I guess the Oklahomans were trying to be polite about it.As far as Nigra is concerned, it obviously is derived from negro with a "nig" thrown in for good measure.