Early wars impossibble?

You can do what you are suppose to be able to do according to the era you are in. So during the Ancient Era you can do pretty much what Egypt, Babylon, etc. did conquer the "world" in your vicinity, later during the classic era you are able to conquer a lot of the world or as Rome did, or the world as you see it, larger than your world in the ancient era anyway. During the medieval with your new economy and all that you can conquer much more, perhaps even so much as Mongolia, it is not the entire world, but it is large. During each era you get the economy and tools to be able to hold more.
I have not problem with economy and early wars. I have many times started a war with the money I got from the scouting, not even have build a caravan yet. Sure as in my example above, it can be tricky with happiness, economy to hold much more than the extra cities taken from the early war.
In my latest game (King), I declared war on Poly very early having two warriors, two catapults and two archers (one of them, originally a scout). I took two of his cities (he had four), including his capital. My economy was not that bad, my happiness was not so bad either. I would have taken the other two cities as well if not he got himself a pantheon (protection) that pretty much ended the war.