The first thing I thought of was group polarization. Variation exists between the human race, variation in ideas (as this website so demonstrates). As people meet others who have similar ideas, they gradually shift to extremes. It's social psychology. Extremes meet other extremes, and they are, of course, unable to come to compromise. This leads to misunderstanding, disinformation, ignorance, and eventually violence. That violence continues and is unable to abate because the original extremes never come to compromise.

Also, the stratification of people across the globe may have contributed to this extremism.

 And I'm sure white people had something to do with it. "Heart of Darkness," anyone?