Original sentence: That a Doric-speaking population entered the Peloponnesus from outside of it and displaced some of the previous population there, changing the main dialect from Mycenaean to Doric, now debated, especially by archaeologists
Edited sentence: That a Doric-speaking population entered the Peloponnesus from outside of it and displaced some of the previous population there, changing the main dialect from Mycenaean to Doric, is unquestioned by historians but debated by archaeologists