How can you build an unbeatable army on Evony?

Answer 1

make 200k archer, 100k Cavalry , 100k Warrior,swordsman and pikesman

There is no such thing as an unbeatable army on Evony. Example: I was recently attacked by an army of 400k archers, 100k cavalry and plenty of others. Of course, it had to attack in waves because you cannot have more than about 100k troops in an individual attack.

My alliance sent me reinforcements and we defeated this army 100k at a time. Actually, the attacker gave up after losing two waves.

You can also attack an army of 400K archers or more simply by sending wave after wave of attackers. Your first several waves will be wiped out but eventually the defending army will suffer enough losses that you will win. You just need to have enough troops in reserve to keep the attacks going. It helps if you have an alliance that will share in the attacks.

If the defender has their gates closed, a small army can defeat a very large army. You just keep attacking until loyalty gets down to 5 and then stop. By now you have taken all their food and their population has deserted so they are no longer producing food. Wait an hour and scout them again. Their army will have shrank due to lack of food. If it is now small enough you can attack again. Otherwise wait for more of their army to starve.