I was led to understand (during my military training) that it was a war crime to attack any state in order to force a regime change. I extremely glad I had already taken my option to leave the services by the time this all kicked off. I have said for years that Blair should be taken to court over this.
In his own mind, he seems to believe that being appointed "Middle East special peace envoy" or whatever ridiculous title he subsequently held was enough salvation for him.