Great power intervention scales better into the late game if we weight it for development

[Mindel]

At the moment, great power intervention lets a great power join a war on the side with the smaller number of great powers to "balance things out". For a certain period of the game, this makes some sense as a model for balance-of-power realpolitik; great powers will be approximately equal in size, with the 1st being roughly two times the size of the 8th.

But typically in the late game, this proportion starts to skyrocket as the human player pulls farther ahead of the AIs. The 1st great power may well be 4x the size of the 2nd power or more. In this case, it no longer makes sense that other great powers would be intervening just to balance out the number of great powers in a war. It would make much more sense if, say, powers 2, 3, 4, and 5 all line up together to oppose 1 from expanding further.

The simplest way to implement this is to tweak the intervention mechanic so that great powers can join a war on the side with the lesser amount of great power development. For the early and middle game, the result would not be very different from the current mechanic. However, as the 1st power starts to widen the lead between themselves and the others, the other powers will be more likely to gang up to knock it back down.

 

[Mindel]

I would also add an additional mechanic that further incentivizes the lesser 7 great powers to consistently go after the Big One using interventions when it starts to hold over 50% of all great power development. In real life, this would be an emergency situation for any realpolitik planner from these countries. Something like a "great power coalition" would be quite warranted.