I have played emperor and won by conquest -- simply crank out barracks, chariots, diplomats, settlers (to build roads) and sail. Enough chariots (attack strength of 4) will wipe out any unit in the game that isn't behind walls, and quite a few that are. If you encounter a city that is too well defended, send in the diplomats to either A) incite revolt or B) sabotage the city walls. Then grind them down into dust.
How to win by space on Emperor? I offer the following suggestion: Conquer the entire world using strategy above until there is one city left. Surround it with a wall of phalanxes. Then convert to a republic or democracy and play a conventional research game. With 50-70 cities producing research, the advances come pretty quickly.
Hmm .. someone asked about chariots in the real world ...
... IIRC, chariots were the tanks of the ancient world. However, they were not nearly as effective over broken ground or in hills, forests, mountains. Give them a nice, flat plain and they were unstoppable. So the other side quickly learned to fight their battles somewhere other than on flat plains and the chariot's utility diminished.
Another problem is that chariots require multiple horses, which are expensive due to the immense demand for fodder. Also, chariots are machines and have all kinds of parts -- tongues, wheels -- that break easily. That's why the knight took over from the chariot -- an armored knight has all the shock power of a chariot, but needs fewer horses, doesn't require as much maintenance and can actually function on broken terrain. A cheaper solution that is actually better. And so the chariot disappeared. Or so I've been told.
Respectfully,
Brian P.