Alastor, any belief that Iwars is a team based game is surely completely destroyed when I sign up?
The whole idea with alliances and betrayals of said alliances is that the majority of what makes up the game with regards this is contained within the metagame aspect. Declaring allies/neutral/enemy is a simple game mechanic to make sure certain things happen in the game but the actual meat of it is all in the roleplaying.
While betrayal is "fun" for some, what I am proposing doesn't prevent betrayal - it just means one would have to be more creative, more subtle, more devastating, since the 'target' would have one Turn to prepare for incoming ...
or it could mean that you're not actually good enough at this game to be able to immediately defend yourself when you suddenly get stabbed in the back (as you haven't done the proper prep work in the game to ensure someone can't irrevocably damage you if they did betray you)? You need a safety net to pre warn you so you have no nasty surprises?

The purpose of *this* discussion is to see what people think of the current set-up, which permits a Starlord to revoke an Alliance without notice ... the results of such revocation can be devastating to a position - and the 'without notice' part actively encourages treachery (with no current downside for treachery) ...
There may be no downside to treachery built into the game mechanics but it is ludicrous to say that there is no downside to treachery. In a full game various alliances and complex relationships all interlink and overlap. Shooting down your current allies main battlefleet doesn't mean that all that happens is that he loses his fleet. You immediately lose an ally and possibly kick off a chain of events where other allies break off relations with you because of your behaviour and it could all come crashing down around you. The decision to stab someone in the back has to be judged carefully in case you ending doing yourself more damage in the long term than you stand to gain in the short term.
I do not envisage carefully planning to pirate my ally's main battlefleet with my much greater force and then sending that starlord a letter which says "Dear Sir, I don't like you anymore and am going to declare you an enemy. This will take effect in two turns. Please don't be suspicious and immediately move the fleet I intend to pirate because it's fairly obvious what I plan to do".
the results of such revocation can be devastating to a position
See my response to Alastor about not prepping your position well enough in the first place

Ever wondered how a US soldier explains to an Iraqi detainee that they are about to undergo a strip search? Till now, we assumed they cracked open a beer and produced their camera, but it turns out the method is way more sophisticated.