Okay, so, I was looking at both this wiki and the UESPwiki for information on the Mages Guild, and I came across a bit of a dilemma: this wiki says the guild was dismantled during or after the Great War, but UESP says it was after the Oblivion Crisis. The UESP cites the Elder Scrolls novels, The Infernal City and Lord of Souls as proof, but I haven't read them and I don't know if they can be considered canon (read somewhere that nothing is canon in the TES universe, and a lot of people supported that claim--but please correct me if I'm wrong). So my question is, was it after the Great War or the Oblivion Crisis? Apologies in advance if this question is comes off as really stupid; I'm not very well-versed in the lore and I'm very confused right now.
That's incorrect. The College of Winterhold lost it's standing as the gem of Winterhold when the Crisis happened, as rather than knowing it was Dagon the Winterholders thought the Mages were doing some voodoo. I'm pretty sure it was the Great War since the Thalmor hate any Man potenitally being stronger in magic (combat too, but magic is their focus) than the Mer.
All we know is the period, not specific time. Its easier to say why it disbanded. Thanks to the oblivion crisis, manimarcos actions during it and the ban on necromancy the schoolnof conjuration was distrusted. This lead to rifts in the guild. One one side there were those who thought conjuration should be banned, and those who thought its ok. Another reason is that it had become all about politics and not learning about magic. It ended up splitting into the Synod (anti-conjuration) and College of Whispers (pro-conjuration) also, the colleg of winterhold has nothing to do with the mages guild