How much army needed to do an attack?

1 troop if the other person has no military. If you want to break then it would be more than what the other person has.

http://wiki.earthempires.com/index.php/Attacking

might be helpful

http://sof.earth2025.net/

These folks can teach you all about this game. As much as you know (or don't know) about this game, you can rest easy knowing that you already know more than a person named,"no1stroker".