having good or bad alliances, betrayals and their in-game justificitions are one thing, while completely unnatural course of events the other.
if you have long alliance with realm A, but they leave you first moment when realm B attacks you, that is already betrayal which needs all kind of in-game justifications and politics.
if, however, realm A not only breaks the alliance but declare war on you, and ally with your new enemy, all within several turns, that is only tasteless play with buttons, such things cannot pass any test of rp-ing sense. not to mention that many even don't care to seek for some justification, couple of mumbling sentences and pressing the buttons is all.
that reduces depth of diplomatic play and depth of game in general. i doubt any medieval background could be found for blitzkrieg wars and blitz realm change of loyalties.
While quick changes of loyalties on level of single noble or even the largest city could have lot of sense (though it is seen very rarely) I see none for realm diplomatic buttons acrobatics.
You speak of a "long" alliance as if the time itself somehow lends weight to it. While it might be a consideration, an alliance of convenience could well last a long time, and be broken either when it first becomes no-longer convenient, or some power grab comes up. Dominic was trying to point out that the duration the treaty has been in play is far less imporatant then factors like how the treaty came about, what has been the current relationship between the allied realms? Take for example FEI. Cathay and GA have had an alliance since GA sent military aid to Cathay during the Great Crusade. Recently GA moved through Cathay lands in order attack another realm, explicitly after Cathay refused them passage through their lands. Should they have to go through some long process just to get a revenge war going?
The problem is you are trying to use game mechanics to solve a behavior problem. Some realms do indeed not take Alliances seriously enough, but the solution you propose limits ALL realms, in order to try and prevent the behavior of some. Besides read up some history about just how greedy and ready to betray each other nobles could be. Take the 100 year war for example. Edward King of England was also the Lord of Gascony, a fief of France. After some argument revolving around one king not wanting to swear homage to another, King Edward finally did swear homage, and kept Gascony and in the process gave up his own claims to the throne of France. Almost as soon as Edward was distracted fighting Scotland, King Philip of France saw the opportunity to take Gascony, after initially accepting the ritual of homage.
Later in that long war, 1356 I think A truce was signed between then kings Edward of England and John of France. Edward took possession Aquitaine in return for freeing King John. The peace lasted but 2 years before Edward again invaded, since revolts and trouble in France led him to believe he could claim the throne.
Given the time differences between the game and real life, in that game time is rather compressed in terms of actual events (nobody wants peace of year and years, or taking years to rebuild from an invasion) I would think this is just one example of how fast the diplomacy of the age could change, and just how little the nobility of the time really cared about honour in the romantic way that we think of it.
