The Imperial Age is medieval warfare at maximum scale. Every early-game unit line has matured, research is deep, and the map has usually settled into contested territory with real front lines.
Because both sides can now field large, well-upgraded armies, the Imperial Age is where army management becomes the differentiator: formations that protect your damage dealers, reinforcements that arrive before the line breaks, and the discipline to trade armies only when the exchange favors you.
It’s also the last era where the old rules fully apply. Industrialization is coming, and empires that spend the Imperial Age building an economy that can absorb that transition enter the next era with a decisive advantage.