I feel this message always gets lost in the sea of "but diversification is doubleplusgood!" You can't have a culturally diverse population and still have a sing

I feel this message always gets lost in the sea of "but diversification is doubleplusgood!" You can't have a culturally diverse population and still have a singular national identity. Have you read about the Lombard invasion of northern Italy in the 6th century? It was essentially a massive, unopposed migration, but the effect was the same as an invasion - the Lomards ruled northern Italy for centuries.