Excelsior

I noticed when I'm being attacked by a mob, the first one I automatically attack, but the rest I have to go into war mode and double click to attack them. This is kind of annoying, and I think it would be nice to automatically attack all of them.
I mean in real life, if you had 5 guys beating you up and you had a bat, wouldn't you hit all of them without really thinking about it much? Or would you stop and think while they beat you "Hmm, do I want to die and attack him... Hmmm..".

It's the way AI works, i wouldnt go change it because the consequences could be dire (like nobody attacking you at all hehe).
I think it's made to conserve CPU time. If all monsters in the world would be thinking non stop about what they can kill, the server would lag a lot. That's why they only look around and think about what they see every 5 seconds. Or, when attacked.

About war mode - if you attack a monster, you can't be in peace mode i suppose These are some standard UO things - it might be different on osi, but all shards that play RunUO have the same system.