So looking at the wiki article it seems there isn't much known about how alliances work beyond that they tend to be formed against entities that make it required to kill neutral factions, yet at the same time I think I have noticed two alliances going to war with each other in my mods, both of which didn't have any members which fulfilled that criteria. Wouldn't that mean there's more to alliances than just the above condition?
For context, I am experimenting with reframing the world's entities. Essentially, the biggest world is the size of Iceland about, and even small kingdoms during the ancient world (Mesopotamia for example) were far more populous than a DF kingdom. But, what if one were to change the naming conventions of entities up so they were called cities and towns (ie a human entity called "The Green Kingdom" becomes "The Green City" and then, if possible, find out what pool names are pulled from for alliances and fiddle with that to ensure it says things like "the Confederation of so-and-so", and if possible mess around with the frequency and probability of alliances? That would allow you to create the illusion of cohesive nations consisting of multiple entities which now function more like districts of a bigger government so long as the alliance holds. I, personally, would like to understand more about alliances to better bring this idea into existence, but I feel a thread generally about the ins and outs of goofing around with this feature could be useful.