I haven't seen any rules for how your new stronghold fits into the politics of the campaign, or how adventurers should handle their villagers and local population, or how to manage a rise in local or national power hierarchy, then I must have missed them in all the years of playing 1e. If they exist, then I stand corrected.
If one really can do nothing at all in the game without being led through it step-by-step in a handbook, then one might have trouble just getting one's character out of bed.
"Imagination, intelligence, problem solving ability, and memory are all continuously exercised by participants in the game". (PHB, "The Game")
Not everyone is necessarily ready for
Advanced D&D, even simply as a text that assumes some prior grounding in the game.
[edit] Yes, Gygax claimed that "it will stand alone", but I think that can hardly be more true than that the DMG "has been written and edited in order to make the whole as easily understood as possible without taking anything away from its complexity and completeness."
At any rate, not everything that is potentially part of the game
could get detailed treatment in the essential books. A great many subjects of interest to particular people got covered in magazine articles and other publications.
It was not the purpose of the text to set "the politics" of anyone's, much less everyone's campaign. See DMG pp. 88-89, "Social Class and Rank in Advanced Dungeons & Dragons" and "Town and City Social Structure".
It was not the purpose of the text to tell you how you as a player "should" do anything, beyond the general advice in the PHB ("Successful Adventures", pp. 107-109). Read, e.g., Machiavelli's
The Prince, if you want advice on such matters.
The books set out defaults for:
territory development by player characters
monthly revenue per capita from trade, taxation and tithes (PHB, by character class)
employment of hirelings, from carpenters to spies
ships and sieges
disease
personae of non-player characters
morale and loyalty
encounter reactions (oddly or not, in the "Combat" section)
... and a lot of other things.