First I should note that I have only skimmed the letters (those guys could write a whole lot).
I found it facinating to note that both felt that long term peace could be established through an international arbitration body formed through a common consensus, I suppose this is not too surprising given that this was the grand plan of the League of Nations formed after the first world war. Freud put it as:
Regarding the world of today the same conclusion holds good, and you, too, have reached it, though by a shorter path. There is but one sure way of ending war and that is the establishment, by common consent, of a central control which shall have the last word in every conflict of interests.
For me the sadest thing about the whole war in Iraq is that we have essentially subverted the key point of the UN, that there is a common consent. I forget which philosopher explored it, but in their exploration of the concept of power, there is power over and power with. The concept of power with is much harder to achieve, but easy to grasp (wonder twins unite etc), and can be very frustrating, but like all things that rely on consensus, if you believe in it you must accept it warts and all (like us voting in John Howard, unfortunate but if you believe in democracy you have to lump it once in a while).