noone has ever captures and maintained 18 supply center's, not since the roman empire and the ming dynasty, and the playing field has gotten bigger.. but after those two great nations did, their regions of the globe were in relative peace, or at least pretty stable until Christianity was introduced to the Romans, and until western Europe starting trafficking opium to the Chinese.
all that aside my actual point was.. diplomacy is just a game with loose rules it was designed as, and is regarded even to this day to be, the most realistic strategy game due to it's lack of a rule strict rule set. Regular diplomacy games do not always end with a clear victor, often actually they don't. Not all diplomacy games stop at 18 SCs, that's just a general sanity saving stopping point. But no matter how good it is, it is not real life I agree, in real life we would be old men sending young men off to die over our inability to compromise. That is the reality of war, diplomacy should be more about compromising and understanding, and less on domination (IMHO). Players who learn to compromise, to give and accept support dominate as a general rule.. players who do not require to win every game seem to be winning more now than those who have to drive for a clear victory everytime.. that's because those players who don't have to win are negotiating the game through the political side of diplomacy and building alliances, and when you identify someone you can work with, why not work with them when you encounter them in other games? i sometimes do, sometimes don't.
i was using that analogy to illustrate this point in a historical context.. a similar context the original game was modeled after. I was not trying to say that anyone should play only based on historical alliances.. that wouldn't be a game, it would be a re-enactment.