Because in the modern world nations trade weapons to each other all the time for profit aswell, would that then mean that the seller of these weapons were at war with any nation that happened to fight the one who bought from them?

But technically it is a form of warfare, but the big players don't want to risk a direct confrontation because of those big, nasty weapons called nukes, which can blow up several cities in one shot and leave a poisonous ruin for a few centuries afterward....its just too costly for the big ones to face off directly...for the moment.

But...if there somehow was a way to not only successfully detect and intercept every missle that your enemy could fire, and somehow synchronize a surprise assault on a global scale to take out every sub and nuke sat an enemy has in one strike...then the bets would be off.

Don't say this could be impossible either, the Ukraine alone has become very good at intercepting most of what Russia fires at them, but some still get through, and in the case of nukes, only one has to successfully reach target to kill millions in one go.