My personal belief is that ethnic diversity and focusing on tribal affiliations is merely the fuel for problems. There has to be an ignition source. The cases listed above all have more in common than simply the existance of generations of ratial, ethnic, or religious hate. For many the cases above that was the radical dislution of the Soviet control mechanism. When the communists "fell" a level of control was removed almost over night. Just as with most teenagers going away to college for the first time, these new free nations could get on with things that have been brewing for generations. Also, the thing that kept Serbs and Corats and Bosnians from fighting each other was the fact that, even though they hated each other, they hated the communists even more. This is why the counter examples of non-communist states comes up. Switzerland, Canada... have not had radical changes in their governements, nor have the people been faced with a complete removal of controling authority. If you notice, most of the ethnic fighting has occured in countries that were once nanny states, where people became accustomed to having the government dictate what was right and what was wrong. Eventually all nanny states will fall, and TS will HTF.
The short term problem that America faces has little to do with increases in minority populations. It has more to do with the ever increasing value placed on the ethnic, religious, ... background of the citizens. As we become more and more hyphenated we loose the ability to control the government, because we become splintered. Simple divide and conquer. Once we loose the ability to control government, then the nanny state will become an even larger reality. The long term problem will be that a few generations form now, it will fall and the control will be removed, then you could end up seeing civil unrest.