I agree with the OP that ultimately the decision to disband a alliance must come from inside the said alliance and no outside force can make it happen. But, unlike many others I think that an outside force can be the decisive factor that led to the disbandment.
I dislike when people bring up FAN, Vox and other alliances into this kind of discussion, because I think it is a bit unfair. [ooc] It is like picking an ordinary soccer team squad, showing them a video from Brazil's national team on 1970 World Cup and saying, "they could play like that so you must play like that too"[/ooc]. FAN et al are exceptions, not the rule. You can't expect every alliance to show the degree of stubbornness, endurance and pride they showed when facing their "eternal" wars. They were/are special alliances, and they are respected exactly for that.
That being said, I believe we can at least partially blame some external power for forcing an alliance disbandment. External powers can create conditions that would torn the fabric of 90% of the alliances out there and lead to their disbandment. The problem with \m/ and [m], as I see it, is that those conditions were not even created. They started a war, they saw that they were going to get their butts kicked and they fell apart, without even trying to survive. If they have fought a few months (that we can and must expect from every alliance out there), were completely torn apart and were still receiving the same peace terms from their enemies and then have decided to disband, I could agree that some outsider played a major role on their disbandment. Since that was not the case, I cannot see any possible way to blame Sponge (besides of course him outplaying them in every field of this game) or anyone else for the said alliances' disbandment.