Got really lucky on this one. We all have mostly the same NPC's doing battle for us. The only difference is if you load assault weapons or not. Usually you don't, just because they use up valuable resources, but sometimes you do.
Anyway, I beat this guy when he and I both had level 11 castles. I was surprised at how much of a crushing victory it was. You're only able to attack with the total number of fighters that each city allows, in the form of their built in defenses. I tried fighting another place that was heavily fortified. I could only go in with 12 NPC's, and my opponent had 153 waiting for me. I had a total defeat, but he lost 7 in the process. Not too bad, all things considered.