Mediation and cultural flow within the context of global interaction (the large scale) are huge influencers of the ‘shape’ of cultural spaces on the small scale. Interactions between different cultural spaces which are far apart from each other (either conceptually or in literal spatial terms; two things which commonly go hand in hand) inevitably alter both. The ideas of each  culture become available to the other as they begin to interact and understand each other, and the specifics of their interactions shape the perceptions each group has of the other, which can then have  enormous consequences for their future interactions, for identity formation, for religion and politics, and for many other aspects of human existence. These consequences can be either positive or negative depending on the circumstances. 
One case of ideas flowing from one cultural space to another which eventually resulted in absolutely disastrous consequences was the case of the Hutu and Tutsi groups in the area we now call Rwanda. When Belgium colonised Rwanda, the white, European colonisers brought with them a certain way of categorising the world, which included the notions of race and racial hierarchy. This fed into (from the outside) very similar-looking ideas about the power structure and the classification of people into different groups which already existed in the local culture. When the Belgians noticed that there were two groups which called themselves ‘hutu’ and ‘tutsi’, and that one seemed to be a more powerful group than the other within their culture, they came to the conclusion that the difference here was a racial one, which is to say, an immutable, biological one, and that the position of power stemmed from the ‘biological superiority’ of the Tutsis. In addition to not being true, this idea  didn’t match up exactly with how the Hutu and Tutsi thought about the topic at the time. None of that mattered particularly much to the colonial administration, though. They continued on with this idea, teaching it in the schools (segregated, of course) that they set up for the indigenous peoples and granting the Tutsis positions in the colonial government, although not granting them authority over whites. In this case, the force of mediation (i.e. the means by which cultural ideas are transferred from one group to another) was schooling. Eventually the idea was totally absorbed into the local culture and thus was planted the seed for racial antagonism. And racial antagonism there was! Tutsi chiefs who were placed in positions of more or less absolute authority within their jurisdictions controlled and exploited the Hutus they ruled over by dictating what crops they should grow and how much, collecting taxes for the government, and taking essentially whatever they wanted under threat of exile. This antagonistic relationship continued to be relevant long after the colonial administration left Rwanda, eventually leading to a genocide of the Tutsis in 1994, in which about 70% of Tutsis were killed.
Mediation and cultural flow don’t always lead to genocide though. In fact, one of the most common outcomes is that people’s ways of identifying themselves, meeting their basic needs, and of entertaining themselves change, and nobody dies at all. Of course, in most of these cases the force of mediation is something relatively innocuous, like television programs, trade, or clothing, rather than an oppressive, exploitative, racist hegemony.
