[quote=@Sigma]
[@Willy Vereb] I do like the idea of some sort of Orbital Defense System shooting down nukes if they were launched. Kinda keeps warfare conventional to an extent.  
[/quote]I thought more along the lines of an intelligent killsat system striking the origin nation of the nucelar attack. That sounds even more like a deterrent. Of course the advanced sensors and AI make it virtually infallible in its judgement (so by storyline purposes it never makes mistakes). It sounds like a terrible enough deterrent that after the first few failures worldwide nobody is crazy enough to work on WMDs in this setting.