Sure, but the "proxy wars" in Korea, then Vietnam, then Afghanistan, etc. showed that great powers could still do an awful lot of harm to each other without openly declaring war. Korea was quite a shock to all who thought the advent of nuclear weapons had really made all war a thing of the past, but Stalin and Mao both recognized that the moral and political restraints in the west meant that no one would be nuking them over Korea.
Yes, there have been wars by proxy. But these are but mere shadows of the horrors of WWI and WWII. They do not fit the 'total war' model.
I am not saying that nuclear weapons prevent indirect wars. Obviously they don't. And nuclear weapons will not protect us from war forever. Eventually conventional weapons will scale up to their power (and some nuclear weapons will scale down in power) and defenses will be made against them. The nuclear weapon will then not be thought of as absurd or overly destructive. Nonetheless, for 60 years (probably an unprecedented period in history) there has been no direct wars between world powers.