“I think ‘demographic displacement’ is better though I still think that we could probably come up with something better than that. Something less abstract and academic.”
You might work ethnic cleansing in somehow. “The Southern people are being ethnically cleansed by immigrant flooding from their own sacred soil.” Or something similar. The term ‘immigrant flooding’ is powerful. Also, “blended out of historical existence” gets at the idea without using the hot button “genocide” word, which we all know is trademarked.