Sorry, Toad, but NK is mostly right on this. This country is far more resilient than you give it credit for. Once it got past the War of 1812, this country has been relatively secure, and could ward off any outside threat. Even if the south had won, the two Americas would have thrived. The heart of America is made of good people, generally known as the "silent majority". The show up when needed, but silent otherwise (think WWII war effort to win the day). The greatest threat to this country was something they couldn't directly affect. Nuclear annilation. The Cuban Missle Crisis and the cold war was a threat from outside our borders.
Regardless of race, the core people in this country know right from wrong (and I haven't heard anybody imply Mr. Floyd was not wronged). Only the fringe elements of society seek anarchy for the sake of looting and dissension. The peaceful assembly that was attemped that first day quickly got undermined by the anarchist. During ensuing rioting did you notice any pastors in three piece suits hurling molotov cocktails? Or anyone middle-aged at all (besided those recording the events). Primarily young and unwise people who care more about stealing a pair of shoes, than the ramifications of being saddled with an arrest record for the rest of their life. The young have always been foolish, and always will be. So expect more riots in the future.
There is a decided political polarization in today's society, but I don't see it manifesting into war. Every one knows the red states have almost all the guns, it would be a rout. The 1960's were far worse of a threat from within. Today's society is far more homogenized than then. All races have decidely wealthy elements in their respective races. There is no longer wealthy whites and everyone else. There's even been a black president. There is hope, realistic hope, today, versus the fight for any hope 50+ years ago. The response this week the next morning after the previous night's carnage, has been all races showing up together to pitch in and clean up.
The police are in place to maintain law and order, and always have been. Because a crime by a cop was the catalyst, they have been warned to minimize aggression which only encourages more rampant anarchy. The National Guard should stabilize things, they are not beholden to the mayor or city council, and should restore order.
As to the Romans, remember that it took several hundred years for Roman Empire to collapse. Approximately twice as long as we have been a country. We are going to be around for awhile, yet.