How to make reusable civilization actions?

Players has 3 type of action cards (Civilization, Military and empire) and they draw and play 1 card per city they control.

Military and Empire actions are "reusable" in a sense that you will for example always need to build troops and wage war. It will never be something that will be finished.

On the other hand, the civilization actions which allow colonization and city growth will eventually reach a point where the whole map is colonized and developed making that action useless eventually.

Since players get 1 action per city, the larger their empire, the more action they do and they could expand exponentially or develop their empire pretty fast. The only thing they don't have control is which card they draw.

So I thought that the solution would be to make the civilization card always useful and reusable. What I thought so far:

- War damage cities, reducing their size which means forcing the reconstruction of cities. Still, it will not affect small towns, unless they can also be destroyed forcing the need to recolonize areas. Or players can optionally raze cities.
- Harvesting: Maybe some resource or income must be harvested with an action then added into reserve to perform various stuff. So harvesting will always be necessary.
- Something new to build: Maybe once the map is fully built, there is something new to build like for example wonders, guilds, councils.
- Comparative tracks: Maybe there could be different level of wealth, culture, prestige, economy that players can level up by building stuff in their cities. But since it's something comparative between players (or since stuff decay with time) there is a constant need of investment and rebuilding.

Any other ideas to make civ actions always usable even after the map is filled up?

Else the game could end when the map is entirely filled, but it's not really something I want, the map should be filled in the middle of the game, it's actually a stage of the game.