Complex sentence: To the north the country faced constant Mongol invasions after the 1240s and although Ivan Asen II defeated the Mongols shortly before his death, the regency of Kaliman I Asen (r.1241--1246) agreed to pay an annual tribute to the Mongols to avoid devastation.
Split into simpler sentences: To the north the country faced constant Mongol invasions after the 1240s. Although Ivan Asen II defeated the Mongols shortly before his death, the regency of Kaliman I Asen (r.1241--1246) agreed to pay an annual tribute to the Mongols to avoid devastation.