Complex sentence: Nazi anthropologists attempted to scientifically prove the historical admixture of the Slavs who lived further East and leading Nazi racial theorist Hans Günther regarded the Slavs as being primarily Nordic centuries ago but he believed that they had mixed with non-Nordic types over time.
Split into simpler sentences: Nazi anthropologists attempted to scientifically prove the historical admixture of the Slavs who lived further East. Leading Nazi racial theorist Hans Günther regarded the Slavs as being primarily Nordic centuries ago but he believed that they had mixed with non-Nordic types over time.