Problem is, that normally it isn't so clear cut. There are many grey areas, such as actions of individuals or a small group within a nation. The nation could deny responsibility for that group, for example a group of bandits. But the other nation doesn't have to accept this, because it's down to perspective. Eventually leading to the old arguments of :
"But X did this! And Y did that!"
Another problem is bans, why do we even bother threatening people with them anymore? They mean absolutely nothing these days. Since people can easily just get an alternate account or simply wait the short period that normally is a ban. So it anything seems more like a reward, a week break rather than a punishment. It would be more effective to take more in game solutions, such as restricting access to plugins or turning them into wandering souls. But again these issues might be for another thread.
For now how about the duration of the raids being 1-1 1/2 hours long? I mean to be honest, it's not like the citizens have to be in the city during the raid. The map is huge, there is always some place to roplelaying in it. In regards to time, how about also once every 3 days? A week sounds long, I mean I agree we need rules for when nations can't agree to make their own. But a week waiting, doesn't make people realise they're at war and war is a bad thing. Not fun wise, but morally.
The whole forced warclaim thing, nah... I don't say this because I belong to X, Y or Z. Forced warclaims always make people rage, causing more drama than is needed. Nation leaders need to sit down and agree on things before going to war, if they can't handle that then they don't deserve to be able to go to war. Sounds harsh, I admit. But if you can't handle going into a single battle without being at each others throats. Doesn't that show you're not mature enough to handle such a simple mechanic?