Re: Domain Level Games
@GreenTongue, please rein us in if this moves off-topic from your original enquiry
From my own experience in playing this kind of campaign on here, a straight domain or strategy campaign is very much a 4x that pits player against player. It's in folks interest to amass a mechanical advantage, especially if they can break away from the pack.
For a federated union campaign, there is deliberately less player-vs-player conflict. But you still need something for them to rail against to make for meaningful choices. What I've found helpful is couching the consequences of the player decisions in plot hooks, and this one pillar of what I mean by narrative strategy. For example, the union tries to build X or recruit Y (or whatever) and that requires a roll (no, or little, auto success). If they succeed well, reward them with flavour about the building or unit. If they're partially successful, they will need to expand further effort and tie an excuse for the failure to the explanation - something they can guard against by another choice. If they fail badly enough, break something.
For the second pillar, name things and introduce people and groups and other human elements to evoke an emotive response - the same as you would in a character-led rpg. Get the players invested in the nation
For the third pillar, provide several plot arcs to set the tempo of the campaign, but be prepared to put on the gas or the brakes as necessary as you gauge their interest. Something(s) to struggle against, overcome, feel a sense of achievement
Let me know if a concrete example would help for any of these