Warnings should not be valid while in an offensive war.

[Pellucid]

Essentially, the legitimacy of your country saying "don't start trouble in this region" goes out the window while you're actively starting trouble in the region.

It would also give players of small nations tactical windows to make moves that larger nations in the region might not be too keen on.

 

[Sharples88]

Warnings are pretty broken as it is. You get no consequence except a -10 modifer with the nation you warned and not joining the war in which they started when you wanted them gives you no prestige/stability hits.

 

[Pellucid]

Yes, this would be a nerf to them.