Does the mixing of cultures have more positive or negative repercussions?
This is actually still an open question debated by social scientists. Until quite recently the conventional view was that diversity is simply positive; mixing together people from different cultures makes them more tolerant, provides greater opportunity, and raises productivity and standard of living.
But some recent research on diversity has reached more unpleasant conclusion: Increased diversity can also be harmful, particularly if people have it imposed upon them. The discomfort and distrust created by forced mixing of different cultures can suppress what we call social capital, the social networks and ties between people that make a successful community. Part of the reason why ethnic ghettos often form even in the absence of coercion is that people have a much easier time building social capital with people whose language, culture, and ideas they share.
The good news is that this effect seems to be temporary; the first generation or two after cultures are forced to mix will be a time of disunity and distrust, but as long as the situation doesn't erupt into outright violence (which, sadly, does often happen), after a few generations people will begin to integrate together and see the benefits of increased diversity without the harms. An important part of this process is the creation of a new, broader identity shared across groups---an identity often provided by their new geography where they all live together.