well
it is too early to say that it was caused by just a simple ethinc clash.
It has revealed the major problem of the fast-growing china----the gap between rural people and urban ones, and the corruption in the government.
People have hated it too much.They are furious and the anger can be easily provoked if they have opportunity.
Just like the 50-thousand-people confict last week in ChongQing.
We might see more in several years.
And our government still don't want us to know as usual.
Fortunately these kind of information always spread on the Internet quickly.