The IGN video above reports that Civilization VI has stepped up the game on the weapons of mass destruction front by including a thermonuclear bomb. These bombs are even more deadly than any previously seen and aside from dropping the cities overall population they can damage multiple cities and leave tiles within a five tile radius irradiated for 20 turns, severely damaging that cities economy for the duration. The missiles can be launched in two ways either via a missile silo that is a tile improvement built by a military engineer or via a nuclear submarine that has a shorter range but has the benefit of mobility and can get right up to a cities shoreline before delivering the massive blow.
I think the general advice would be to either deny your enemies a supply of uranium or just buddy up to the world’s nuclear powers. Either way I can’t wait to see Gandhi delivering world peace in his own special irradiated way.