The problem here is basic humannature. Human beings are naturally social animals. We just love being with one another. However when there is an division, artificial as it may be, we get anxious, angr, and violent because such division is against our instinctual nature but it has such a strong pull for we learn this division as a very young age.
We become angry at ourselves but unknowing where to place this anger so we pklace it right on the shoulders of the so called racial divide and get a us versus them mentality.