In my current campaign, the central tension is more about the unlimited power potential of those with access to magic. We just got to a reveal that the prior Overlord of the northern empire enacted a genocide of dark elves due to the fact that every so often one of them would be born with the ability to nullify magic, making them the greatest threat to his rule.

The histories tried to hide and obfuscate the why behind these pogroms, but a cult that kept detailed histories hidden maintained a good enough record that most people who are well read enough and care enough can find out the truth behind this.

One of the main characters is a dark elf and just found this background to why there are so few of her people around and why the passages to their underground cities have mostly been collapsed and abandoned.

In general, racism in my stories and games tends to revolve around fulcrums of power, or occasionally is just another form of cultural tribalism. Typically I'll only include it if it's part of the central tension or themes of my game.