Updated: The population of the muggles in the wizarding world compared to the purebloods is ten times lower. Half of the wizarding world has been empty, the pureblood system runs in the wizarding world everywhere, but again there aren't enough people to run it wholely. Rose's given a mission to investigate the dissapearance of these muggles. The mission explains the torturous and horrible crimes done by the group. Please read it. There's a lot to unpack in the description.