Jesus, I hate this mission, cause it took so long to win this mission. You have to rob all weapons you can get. You have to "rob" also some wood from the island in the north. Build enough ferrys and houses to bring more soldiers to every island. You also have to build some warehouse for gold to increase your combat power. The rest as always – tons of soldiers to one tower, stay there and attack this tower till the enemy soldiers walk into your sight and attack them.