balance - How can the lategame in a 4X game be made more exciting?

I played a lot of different 4X games lately (eXplore, eXpand, eXploit, eXterminate, like the Civilization series, for example), and noticed that most of them suffer from the same problem: As soon as one player got significantly more powerful than the others, that player gets almost unbeatable. The dominant player has access to vastly more resources than the others. Also, that player has a significant advantage in research, which means that the other factions will soon fall back in technology, giving the powerful player even more tools which the weaker factions can not counter, so it makes the game even easier for them.

During this phase it is pretty clear that this player will inevitably win. However, the game usually does not stop here. It continues for hours while the dominant player steamrolls all the weaker players one after another. This poses no challenge to them, because they are so vastly more powerful. So this phase of the game becomes a dull and boring chore for everyone. The dominant player moves their units from one enemy base/city/planet to another knowing that nothing they could encounter there could stop them as long as they avoid some easily avoidable mistakes, while the other players watch helplessly in frustration without any way to prevent their demise.

How could a 4X game be designed to avoid this boring and tedious endgame?

Answer

This is a difficult question to answer objectively, but I will try to construct a solution to your problem without guessing:

You describe the problem at hand as an end of competition to one player because that player became too powerful. Note one thing, though: The player became powerful by terms of the balancing incorporated in the game, so either you change this balancing completely, or you change the "rules" for this state of the game only.

The first option may not be what you want, because the early game was not part of your critique and seems to offer a fun and exciting gameplay. Additionally its hard to construct a change of the whole game balancing targeting only this aspect.

So lets see how we can set rules for only this state of the game. We need to find something that "punishes" overpowerful player(s) by making their life harder or by supporting other players. I have a few examples for you, that can fit this description:

1. 
   

   Cheat. A lot of games use "random" events to bring life and alternation to the world. Some of those are beneficial and some of those aren't. Example: Sim City Catastrophes or Mongol Invasion in Total War. A lot of games have catastrophes that can bring additional challenge to players. You may be able to "randomly" challenge the leading player with a lot more of those catastrophes. But be careful, in Sim City a whirlwind destroying your beautiful city may have been the only challenge for a perfect player, but it can be equally frustrating.

   
   


2. 
   

   Something similar but more predictable may be better to maintain fun at last. You could add not only benefits from having a lot of cities under control and being far the most developt nation, but insert new problems that occur. Large cities are more likely to develop spreading diseases, a big nation is harder to control, more revolutions occur, costs for a lot of armies could skyrocket. These problems are especially able to punish players that expanded or explored to fast, without proper preparation.

   
   


3. 
   

   No other player is a challenge for your leading tyrant. A scary situation, especially for the other players. From my own experience I can say that humans can be pretty careful to avoid this type of snowballing incontestable player. Every time I play something like Risk it is not only my task to become the most powerful player, but instead to seem like I'm doing bad. Because if you are clearly the candidate to win a game, others will start working together and bring you down. Which can still be a threat for you, even though you are leading the board. Total War: Shogun 2 used this technique and totally overdid it. In that game, if you have a big number of territories under control every single clan starts beating you, if you aren't prepared to win fast after that happens you often loose for good. Diplomacy stops working for you. This could be something realistic to use, even though I would advise to balance it properly.

   
   
   


4. 
   

   My last idea is the only one of the type: Support the other players. A lot of 4X games have neutral factions that are to be conquered or to be worked with. While some of them surely like to work with the best-paying/most powerful player on the board, some might resent the idea to be overrun as much as normal players do and might start actually working together with smaller nations in new ways, or even voluntarily become part of them.

   
   

A combination of the techniques may help you balance out your game. But be aware, a game needs to have an end, you might prolong the game for good or make it more interesting, but if the result is always the same as before, or you totally destroy the fun of being the most powerful, you might have just created new problems.

Still I think your idea of keeping up the challenge is not bad, maybe you even make it "impossible" to win alone and increase the value of diplomacy.