Unlike the Horde (as we discussed last week) there have really only been two Alliances. There was the Alliance of Lordaeron, formed by the human kingdoms of the northern parts of the Eastern Kingdoms, the Wildhammer dwarves and the refugees of Stormwind (and later joined by the dwarves of Khaz Modan, gnomes of Gnomeregan and the high elves of Silvermoon) - this Alliance ultimately died many small deaths as members left. Gilneas over the establishment of internment camps for orcs rather than simply exterminating them and the expense of maintaining Nethergarde Keep, Stromgarde over Thoras Trollbane's argument with Terenas Menethil over Trollbane's wish to simply execute all orc prisoners outright. The high elves of Quel'thalas left as soon as they reasonably could after the death of Anduin Lothar, since they originally only joined the Alliance due to an ancient oath to the Arathor bloodline, of which Anduin Lothar as the sole survivor.
It was the rise and fall of this Alliance, which came together fitfully, was nearly destroyed by betrayal, and ultimately died not from defections or secession but by the hand of the man born to rule one of its kingdoms that created its successor. To understand the Alliance of Lordaeron, we must understand the First and Second Wars.