How to Win?

I have more or less figured out from other peoples' posts how one is supposed to win in 3 of the possible ways (though I've not actually won anything yet) -- but how exactly does one win via diplomacy?

1. Magic: Research Master Spells (which tech is very unlikely to show up until you've researched Magic several times after Expert Spellbooks) and cast the Spell of Something-or-other.
2. Questing: As outlined in the Adventure/Domination tech posting, research Quest of Mastery and carry out the appropriate long involved quest.
3. Conquest: Conquer all major factions (do you need minors too?).  Various people have given their own strategies for this in various postings.
4. Diplomacy: I know a few ways to improve your rating with other people (have a bigger army, lots of diplomatic capital, arranged marriages, be of the same faction), but how do you actually win?