Tinpot theory: The only divide that really matters is the wealth divide. Anything else - politics, race, sex, etc. does not have any impact if you are part of the uber rich - you have fuck you money and can do what you want. You can not say this about any of the other divisions. The people who own the media, corporations etc. constantly pit the lower classes against each other by focusing in on these less important divides to keep them busy hating each other while the rug is swept from under their feet. Income equality grows year on year. Your rights are removed year on year, with the fear mongering around the less important divides used as an excuse to do so. Surveillance and control increases through the same means. Could it really be as simple as keep people busy hating each other so they leave the uber rich alone?

In a more general sense though there are lots of parties that would have interest in sowing discord. Divide and conquer can seem like a cliche but that's because it works lol.