As far as I can tell, by the time you get to the modern age the game is in its final stages. But maybe that's just because I haven't played enough games.
The modern age makes several victory conditions quickly available:
- UN for diplomatic, which could happen at any time a vote goes well.
- Apollo program for space victory -- basically if you're even or lagging in tech, it's a race to finish the spaceship. If you're ahead, you can take your time.
- Cultural, since by the time you make it to modern you're approaching these thresholds.
Conquering or dominating is usually less of an option at this point because you've established an uneasy balance to make it this far. If either actually is an option, it's probably because you're so far ahead already that it's just a matter of sweeping up the pieces of the remaining civilizations.
--Yelof