Yes, Ibn-Khaldun--you're exactly right. A neutral army passes through your land, you tell 'em "get out of my soil." My diplomat ought to be able to do this. I subscribe entirely to the idea.
Yes, Caledonian Rhyfelwyr--you besiege a town for years, then your diplomat tells the mayor or baron, "Let's end this madness and surrender your ruins without further ado." Great idea!