Well, the way I see it unless your playing the Romans, your trying to declare the war at the wrong time. (Assuming normal speed).
You either need to play a rush strategy or wait for dominating units. (Normal Swordsmen just aren't a dominating unit against opponents with access to either Cooper or Iron since Axes are adviable so much earlier.)
The standard Sword rush tactic is:
1. Found a city or two.
2. Find an opponent WITHOUT Cooper
3. Make Baracks a much higher priority compared to normal.
4. Discover Iron Working early
5. Build Swords with CR promotions.
6. If your opponent has Iron near them attack BEFORE they can connect it.
10 to 20 units sounds excessive, you just need a big enough stack to take the first target. Dig in there while reinforcement arrive.