The problem is that all nations don't have nuclear weapons. Some nations are nuclear weapon free zones, inviting an attack from other nations. If all nations had nuclear weapons there would be no fear of one nation attacking another.
In addition, if all nations equipped their citizens with smaller tactical nuclear weapons, neighborhoods would be safer. Neighbors wouldn't attack each other.
Better yet, if we equip every citizen with really small nukes, they can carry them to church, school, theathers, shopping malls, cars, and everywhere they go. There will be no personal attacks.
So, the answer is crystal clear. Equip everyone with nuclear weapons. All attacks will stop.
World peace will be acheived.
It's a no brainer.