Diplomatic Campaigns

Plan based on event not Based on location.

Also work on your NPC'S don't let your players feel to much more powerful than the NPC's or they might just kill whoever they think is guilty.
They shouldn't be able to just easily barge into any important building's

A neat trick is to steal mechanics from board games
Political can are ultimately about economics, a subject not well modeled in TTRPG.
So use Catan or Lords of Waterdeep to gamify NPC strategy and goals

I’ve lately been using Blades in the Dark for its faction game. Factions have goals, progress clocks, opponents, allies etc.
There are tiers for each faction that can change and affect difficulty of moving against them.
A lot of the faction game parts of Blades in the Dark are hackable into most any system.

Randosaurus is dead right about the board games, a good shout there!

I've had a fair bit of political shenanigans going on in recent games, which my headstrong group of adventurers are starting to find themselves embroiled in. Heres a few things I'm trying out:

- Multiple lines of "reasons for doing", and potentially conflicting or hidden motives within all the various groups involved keeps the Players on their toes. The Lord of Town A asks for help chasing down a criminal who has done something terrible and gone to Town B: but Town B is lawless and full of criminals, and real cesspit, everyone here must be bad; but the criminal they are chasing, turns out they know the Lord from Town A pretty well; infact, they once worked together. Who to believe?; maybe they did, but maybe it was not as black and white as that. And so on and so on.

- Different perspectives work well too. As you could have a totally righteous Lord who is looking to build schools or whatever, and believes they are doing the best thing for their people, who they care about. But, word in the fields is that the Lord is a demon, a man possessed, sending bailiffs round and upping taxes unnecessarily. And that bandit problem? maybe the Lord's tax rises led to those farmers becoming bandits?

- Also, having NPCs as fully formed characters, at least the ones involved politically. This means that they can change their views, positions or even ideals eventually, and naturally. This also means that if your Players find a way to manipulate or heavy hand a situation (especially if they resort to intimidation or the like) then they can end up turning friends into enemies without knowing. "I intimidate Princess Lovely into agreeing to help us cover up our past indiscretions, because she owes us one from freeing her from that castle." Princess Lovely, the one who was so indebted to her saviours and promised them the world, has a vicious streak in her and does not appreciate upstarts telling her what to do. She sends the Party off to a near suicidal mission under the pretense of treasure that doesn't exist.

- Having a mix of types of political characters. Maybe one seems a push-over, but will send people round to have you killed. Maybe one is headstrong,
and stupid, but loved by their people. Maybe one tells the Party what they want to hear, befriends and then betrays them. Or maybe there are just a good person, but they aren't great at their conversations and come across and something negative. Too much of "Good guys and bad guys" will have your Party resorting to violence/intimidation/persuasion as soon as they meet someone they presume is bad, without allowing for actual talking and diplomacy. The grey area is the best place to live.

- Finally, having consequence for actions. So your Party are decided to chop up the Lord that spoke back to them, or maybe just bulldozed through the town and left. The Town Guard there were too scared to do anything, so the Party are off and free and looking for the next place to cause trouble. But maybe news travels fast, and maybe the next town, or the next ten towns they arrive at are abrasive, maybe they get arrested, or that quest that they were on suddenly hits a curve ball. "We need in that high walled city with the thousand guards and battle mages, but they won't let us in because we murder hoboed that town." Well, they can't fight their way into that (maybe) and they will likely realise this. So your super headstrong group now need to take a moment, reevaluate, and maybe apologise? And all this can be flipped into the positive for a good job (villages heralding their arrivals, treasures gifted etc etc)

Anyway, it's early and this is maybe/definitely a ramble, but diplomatic scenarios are great fun and will curtail any group into thinking with more than their sword.