Here frequently are mentioned, that blacks (negroes) are an issue. Interesting aspect is, that Saudi Arabia have quite a lot of african guest workers. But they keep them on "short leash", so they are trying to behave. Because of their physiology, africans are quite resilient workers in scorching Saudi sun. In temperature, which for eastern european would be debilitating, for africans it is just another thuesday.
Even in some african countries, there are developed methods how to keep them orderly enough. Research about Rwanda. Quickest growing economy in Africa. After civil war and genocide. But they found a way how to keep them in order.
So I would more tend to think, that its is not as much that blacks are a problem, but that this "slap on a hand" attitude allowed them to spiral out of control.
Here, where I live, we have around 1/4 of russian speaking population. In jails, de-facto language are russian. For some reason, they commit crime in higher percentage than natives. Most of ethnic russians are just normal people, but still, those crime oriented retartds are in slighly higher numbers than in our native population.
In city where I live, around half of police forces are from ethnicaly russian speaking population. They don't have an issue to beat with batons some other russians, who does not behave. Like, drunk breaking some childrens playground equipment. In result, overal crime levels are kept in check, and most of homicides which happens, are among alcoholics themselves. And most widespread crime, is some shit stolen from car. Assault on person are quite rare.