Neonchameleon
Legend
1) Read Planes of Law, Planes of Chaos, and Planes of Opposition, heck, just read pre-4th Ed D&D lore.
Belived it or not I have The Planewalker's Handbook on my bookshelf. And more pre-4e books than 4e books. I know much of the pre-4e lore (not all of it of course - with the splat bloat TSR put out that dwarfs anything WotC have ever done ther is no way to do so). And I still prefer the 4e cosmology for anything except a pre-Faction War Planescape game.
And the MM1 has plenty of lore in it. I can make a convincing case that it provides me with more lore per monster than the 2E Monstrous Manual It's just written dryly and with relevant details in play and evocative details and a lot of subtle psychology rather than with %Liar chances and ecology.