We haven't seen a major nation-state conflict between nuclear powers since nuclear weapons were invented. Of course there's no counterfactual, but it does seem given the state of relations with Russia it's likely that sans nuclear weapons we would have had a major conflict with them at some point. Also, try reading this, it's a decent summary of nuclear strategic thinking: http://www.amazon.com/The-Bomb-A-New-History/dp/0061537209