4X games (e.g. Civilization, Master of Orion, for this discussion I’m also counting Paradox-style grand strategy like Crusader Kings, Europa Universalis, Stellaris) have a well-known problem where, once you get sufficiently far ahead, you’ve basically already won and the game stops being very interesting. There have been various attempts to fix this, but the problem remains. (Extra Credits had a good discussion of why this is difficult to design around.)
One idea for fixing it could be to change the victory conditions as the game moves on.
Consider that the Civilization series has traditionally been very focused on warfare and conquest, even though they have introduced a lot more peaceful content in the recent versions. But it still tends to be profitable to take over your neighbors if you can.
Now a game that’s very focused on conquest and warfare makes sense if it’s a game set in the period of say Ancient Rome, where “will a more powerful ruler conquer my empire” was a very real threat and something that a ruler in those times *would* realistically have been concerned about. And this remained true for a long time.
But the closer that we get to the modern day, the less true this becomes. Being taken over by an invading army simply isn’t something that the rulers of most countries would be concerned about, these days; the things that they do care about are entirely different. So for a nation-management game set in the modern day, unless it was also set in one of the few conflict-ridden areas that still exist today, warfare being a major focus simply wouldn’t make much sense. Things like economic competition and maintaining the quality of life for your citizens are much more important.
So you might be able to have a design that emulated this. In the early parts of the game, you would want to focus more on conquest and growing bigger to avoid being taken over by your neighbors, as in the current games. But as technology developed, conquest would slowly cease to be a viable path, as entirely new game mechanics took its place. This would gradually eliminate the advantages that you got from your early-game success, but it shouldn’t do it so fast as to make them meaningless. Rather it would give you a leg up as you raced to adapt to the changed conditions, and pivot your old advantages to match the changed conditions before they became just a burden. (In the end, if you didn’t play your cards right, your big huge country would definitely still be around, but losing in score to those pesky little Nordic-analogue countries with small homogeneous populations that kept topping all the quality of life scores.)
I recall seeing some board and card games that simulated something like this: early-game, early-history advantages which give you a leg up but don’t guarantee victory if you don’t keep up in the tech race and changing conditions. Innovation comes to mind as one.
One interesting way of doing this in a computer game might be to take a page from the book Seeing Like A State and its discussion of legibility. Early nations were not very legible to their rulers: the rulers might have only had a very poor idea of how many people lived in the nation, or how much food different farmers might have been capable of producing (and thus how much you could tax them). The book argues that much of history has been a constant drive by rulers to increase the legibility of their realms, by implementing things like a census, standardizing measures, forcing people to adopt family names, and so on.
This ties nicely to what Extra Credits considers the two main problems in making strategy games interesting in the long term: accumulating bonuses, and the constant reduction in uncertainty. In a game like Civilization, you start with a lot of uncertainty, as the whole map is unexplored and you don’t know anything about your local terrain or where your opponents are. As the game advances, there’s less and less that you don’t know and which you would have to address in your planning, and the game essentially becomes a puzzle where you can just figure out the best strategy and then execute it.
Now consider a game that implemented legibility as a game concept. What this might mean was that at first, the game would only model the things that you as a ruler roughly knew about. For example, you wouldn’t know the exact crop yields produced across your empire, so each city would produce the same amount, simulating the fact that you only basically know the nation-wide average and couldn’t do much to affect it.
When you developed technologies that increased the legibility of your empire, the game would randomly assign the different cities a number of variables (e.g. properties of local terrain) that collectively determined how much the different cities actually produced. This would then be revealed to you, letting you start managing them more closely, and thus making your realm more powerful. It would also force you to rethink possible existing plans for the locations of future cities, since the more detailed information about local terrain and its impact on crop yields would now become generally available. Thus what looked like an excellent city site might turn out to be a horrible one, and vice versa.
This would maintain a kind of strategic uncertainty throughout the game, as on each step that your realm got more legible, you would get a bunch of totally new information thrown at you that you had to adapt to and rework your plans around in order to stay competitive. And as there was more and more peaceful economic stuff that you as a ruler could start getting involved in, the military stuff would gradually start declining in relative importance.
Kalle Viiri mentioned the Colonization games as a nice slightly different approach to this: given that the goal is to be the first colony to become independent, being the biggest isn’t necessarily the thing that wins you the game. Rather, being big and powerful does benefit you in colony vs. colony wars, but a smaller colony is easier to defend when you declare independence and end up in a war against your home country. Similarly, the mechanics of how independence support works means that a big colony has a harder time getting to the point where you could actually declare independence. That’s another take on a similar idea: that growing larger and bigger gets you advantages in some areas, but that doesn’t win you the game by itself, and in some ways it’s even actively harmful to winning the game.