And they and their crime -- and that of all of the others covered in your your rant -- were taken to task by the machinery of America's Civilized, Judeo-Christian-Based Rule of Law and, as they FRom time to time pop up, still are.
But wherever that machinery has been and/or will be placed into the hands of those who, whether in Rhodesia, Somalia, Suid Afrika or in Detroit, are intellectually and/or Morally ill-equipped for the responsibility -- and who are otherwise-motivated -- the destruction of all of Western ["Human," that is] Civilization's Gains inevitably occurs.
That was no " rant ", it was refutation. Shall I call what you type , " rant " or can ?
Look, I don't want to argue , I am upset by what's happening in Zimbabwe, scared to death about what has / is / and in all probability shall happen in South Africa. I also KNOW what has historically happened and is happening now, in the USA. The places aren't at all similar and neither do they share a commonality of historical events .A Marxist, black take over, of America isn't in our future. For starters, they don't have the numbers. Secondly, even the MOST diehard white Liberals, aren't going to help elect an Al Sharpton , Louis Farrahkan , Jesse Jackson , etc. president. The government doesn't yet censor / run ALL of our media , and even rabid , white Liberal talking heads won't support the likes of the above. Will Hispanics and Asians ? Not bloody likely. They have their own agendas.
Now,for the crime issue / political corruption . Yes and no ; criminality wasn't punished quite so well, as you seem to imagine it was, decades or even centuries ago. That is historical fact, whether you like it ( know it ) or not.
Rashly pontificating spurious / groundless speculations, and then lambasting well thought out refutation, doesn't make your position stronger. In fact, it considerably weaks your case. Detroit is a hell hole. So are other American cities. So are cities in England, France, and most other places I could waste time on typing. Does that portend the eventual copycatting of what has happened to Zimbabwe ? No, it most assurredly does not. What happened in Zimbabwe, is closer to the Stalinist USSSR , than it is to other places. It has wiffs of Nazi tactics ; however , it is even closer to the events in South Africa, when Zimbabwe / Rhodesia was still part of that country and mfecane / difaquani,tribal wars , treks , and black nation building were all going on. That never happened in America, amongst blacks. Canada, Mexico, and Cuba aren't going to step in , as Lybia,Cuba, South Africa, etc. has , in Zimbabwe , should your scenario even have a distant glimmer of a possibility here.