 The imperial army invaded the Papal States under the command of <unk> of <unk> in October 1228 . Although John defeated the invaders in a series of battles , it took a counter @-@ invasion by another papal army in southern Italy to drive <unk> back to Sulmona . John laid a siege before returning to Perugia in early 1229 to conclude negotiations with envoys of the Latin Empire of Constantinople , who were offering him the imperial crown . 
