Preface: I posted this on theRPGsite about three years ago, and stumbled across it while searching for something else. You may see some hints about where I developed my formulation of the the swashbuckling 'endgame.'"Building a stronghold" is more than the construction of a castle and hiring of mercenaries. It's about becoming a political creature. I think this is what many fantasy games miss, and it's one of the reasons I prefer historical games to fantasy ones.
For this to work, the players must accept that the goals and objectives change as the game transitions from one style of play to another over time. To use a hex-and-counter analogy, it starts off as GDW's The Battle of Agincourt and becomes Avalon Hill's Kingmaker.
From what little I've read of the early days of fantasy rpgs - mostly The First Fantasy Campaign - the players readily understood and embraced this mindset. From my own experience, however, it disappeared pretty quickly among gamers: in our AD&D games in the early Eighties - call it '81 to '83 or thereabouts - building a stronghold was about clearing land and building a castle and hiring mercenaries and attracting followers [and] was followed by fighting off monsters and humanoids who wanted to make that stronghold their next lair and those followers their next meal. The political game remained nebulous to non-existant, in no small part because our strongholds tended to be built beyond the frontier, consciously or subconsciously reflecting the desire to avoid being beholden to a prince and the attendant political maneuvering. Our experience was more like a cavalry outpost in Indian country than the War of the Roses.
Accomplishing this means enmeshing the adventurers in the political world of the setting, which of course means there needs to be a political component to the setting first. I didn't really grasp this until I was in college, so it started appearing in my games in the mid-Eighties; the relationship between a planetary government and the Imperium in my Traveller games began taking on some nuance and balkanized worlds became my favorite planets for adventure, frex.
Kingmaker provided a lot of inspiration for introducing politics into my roleplaying gaming. Power is gained through control of offices of the state and church, not just nobles and men-at-arms in the field; if one's faction does not possess the sole prince, then one needs to crown a pretender and gain seats in the houses of Lords and Commons or one may be quickly isolated and overwhelmed when Parliament is summoned.
The key idea here is that one's ability to exert influence in the setting must extend further than the point on one's sword or lance, so gaining political power means gaining entry to and mastery of the institutions of state. In a fantasy roleplaying game, this means giving the adventurers the opportunity to join something, to climb a hierarchy other than the experience points table, to gain titles other than those of one's class. It could be an order of knighthood, a college of wizards, a religious confraternity, the Thieves' Guild, or whatever; as the adventurers gain personal power, they should have the opportunity to gain influence as well. A career spent as the behind-the-scenes mercenary strike force of the Emperor doesn't get you there.
By the time they reach "name level," or whatever level represents the lower reaches of the game-world's main figures of power, they should be enmeshed in the affairs of state, able to enter the halls of power and reasonably expect to pull some of the levers therein.
The situations they confront there should not be readily resolved with swords or spells - at least not always. One should need allies, and one should be someone who is sought for an alliance. This means the referee needs to create, and run, a convincing court with conflicting factions as well as allies and enemies abroad - and if those allies can sometimes be enemies and vice cersa, so much the better. The adventurers graduate from simple power wielders to power brokers, using those levers of power to exhance or diminish the levers pulled by others. A fighter who is also the grandmaster of an order or knights and the governor of a royal fortress controlling a key pass in the mountains or a cleric who is the ecclesiarch of an important temple and the tutor to the prince's heir possess the leverage to affect events out of scale with their stats and abilities.
Once you reach this point, in my opinion, the "historical scope" of the campaign becomes tangible and meaningful to both the players and the adventurers. Can your character become a Warwick, or a Richelieu?
This doesn't preclude the characters from reaching higher by any means. The adventurers in this game can also aspire to be a Timur or an Othman, but they may find that gaining an empire is not the same as holding it. A prince often discovers that there are levers of power out of reach of the throne, so one better gain, and keep, allies. The idea of legacy may become a powerful motivation here: Othman established a great dynasty, while Timur's empire pretty much died with him.
For this type of play, one where the characters control considerable resources by dint of office or commission, counting gold pieces needs to be abstracted.
To borrow an analogy from another board game, you need something like the BRPs - basic resource points, iirc - of Third Reich, a simple means of representing the resources of a city, a realm, or what-have-you, and a mean of converting them into armies or fortresses or school or temples or estates. The ability to give power as well as the mean of gaining it should be important at this level, such as placing a henchman in a key provincial government or an admiralty; rewards should be more than, "Oh, and here's this +1 sword I don't use anymore."