The Uprising of Asen and Peter ( ) was a revolt of Bulgarians and Vlachs living in Moesia and the Balkan Mountains , then the theme of Paristrion of the Byzantine Empire , caused Causation by a tax increase .

Thus , when the armies of Bulgarians and the Vlachs returned Arriving , reinforced Cause_change_of_strength with their Cuman allies , they found Know the region undefended and regained Getting not only their old territory but the whole of Moesia , a considerable step towards the establishment of a new Bulgarian state .