This is what I loved about Empire Earth.
You'd start as Cavemen and need to build up your economy before transitions to the next age. You might be able to get lucky rushing with some Cave-Soldiers but if you were too slow your rock-throwing would get rolled by arrows.
So then the game turned from a military race to an expansion and economy race to move to the best age as quickly as possible. The maps were soooo big, but borders would be defined in early ages, so eventually you'd bump with your neighbor.
Then the negotiating starts. Alliances and resource trades - could be broken at any time but 2 Bronze Age better than 1.
I miss slowburn RTS. I hate the big person on small map look of Age of Empires. I wish Manor Lords woulda been dev'd harder into a solid RTS game, now that's a big map.