Why does the US have such high racial tensions?

It is only in Democrat run cities .  The people there have been lied to over and over about how the politicians are going to help them, then see you next election .  

i think thats everywhere, not just in the us

Because it's a failure in so many ways.  Too many police and prisons, not enough welfare or housing.

Because there are too many racists and liars.

The liberal media complex wants race riots that’s why they keep showing the moment the cop kills George Floyd over and over, night after night, despite the riots, looting, and fires. Fox News obviously wants Trum gone too. You can’t watch for fifteen minutes without seeing that cop kneel on George Floyd’s neck.

Because Diversity is not a strength, it usually precedes war, and because Race is not a social construct. It's scientific fact, and has serious ramifications for society.