Stuck in campaign

I'm at the stage of the campaign where you gather your armies and go after the Fallen.  I attacked and defeated the Fallen general and his "pet", but now I'm stuck.

The only thing I see in my campaign log is "gather your armies and go south to kick butt", and I can't go further south past where I defeated the fallen forces, even though I see unexplored area south of where the fight happened.

Is there a bug, or am I just missing something obvious?