I'm at the fourth shard.
I'm surrounded by the conquered territories of a my ally, a good wizard. What should I do? Attack him or sit around exploring dungeons?
Thanks.

Well, that depends on your situation. If you're not strong enough to fight him then you should explore for a while. If he manages to kill the other opponents on the shard then he'll declare war on you eventually, so be prepared!

Thank tou very much

No problem. Another thing that I forgot to mention; if someone else defeats a lord then all of his lands will turn neutral. If you're on one of the lower difficulty settings this can make the lands much easier to capture.