... The outbreak which originated the second Bulgarian Empire was occasioned by the exactions of the Emperor Isaac Angelus, who collected taxes with extraordinary rigour in order to meet the expenses of his court.  The two brothers Asen and Peter, having in vain demanded redress, proclaimed a revolt, and announced that St. Demetrius had left his shrine in Salonica, and, as a sign of special favour, taken up his abode in Trnovo, where they established the capital of their new state.  The superstition and grievances of the peasantry assured them a favourable hearing; the Bulgarians rose against Isaac Angelus and successfully resisted his attempt to subdue them.  But the national tendency to dissension asserted itself.  Asen and Peter were both assassinated, and were succeeded by their younger brother, Joannitza or Kaloyan (Good John), whose natural abilities and exceptionally favourable opportunities enabled him to put the Bulgarian state on a former footing... (Turkey in Europe, Eliot, 1908)