Uh, no, if several hundred thousand people were murdered, that would be a massacre.
If they left because they were afraid of being murdered (or otherwise violated in their physical safety), that would be ethnic cleansing.
Do you not believe this applies to those who left Detroit, or Algeria? Really? Is it not the case that every country and major city outside East Asia contains areas where residing would endanger you? Including... most of Detroit? Could you seriously be this good and innocent a person?
Note also that it takes a lot less physical menace to drive out Ward and June Cleaver, than Dylan "YOLO" Hipster. Of course, Ward and June were privileged...
Crime isn't force? Withholding protection from crime isn't systematic?
When Milosevic went to cleanse Kosovo, he didn't send the Yugoslav Army to put people in cattle cars. He just let Arkan's Tigers do whatever. Arkan got the message and so did the Albanians:
I'm not sure what to make of you comparing several hundred thousand people moving to a new location to a mass murder.
Do you somehow think that deaths from murder were a major contributor to the changing demographics of Detroit?