That was the takeaway for me too: the movie was only tangentially about apartheid but it was also about slavery in the South, the Trail of Tears, the brutality that man can show to fellow sapient creatures but also the nobility and magnificence. The hostility shown by the humans -- white and black -- to the aliens hammers home the point that the general dynamic is the same throughout history, what changes is the line of demarcation which dictates who is "one of us" and who is an outsider.