Tsar Ivan Strasimir's state spanned the lands between the Timok and the Iskar. He was crowned Tsar in Vidin at the request of his father Ivan Alexander. During his lifetime he had attempted to settle the relationship between his two sons from different marriages by making the elder one ruler of the northwestern Bulgarian lands. However, distrust and resentment persisted. In times of ordeal, Ivan Sratsimir and Ivan Shishman failed to come to agreement, making things easier for the conqueror.

Ivan Sratsimir has been the subject of much debate by historians. Was he an able or a mediocre ruler? Either way, however, the tiny kingdom would have been too frail an obstacle to the advancement of Sultan Murad and his successor Bayazid. In the spring of 1365 the Hungarian king Ludovik overran the tiny kingdom and incorporated it into his state, taking the Bulgarian ruler captive. Ivan Sratsimir was imprisoned in Croatia and forced to convert to Catholicism. Several years later Ivan Alexander, assisted by Vlach troops, restored his son to the throne. After his father's death in 1395, Ivan Sratsimir became a tsar in his own right.

In the two decades that followed there is no evidence in the chronicles of successful military campaigns against the Turks. Conscious of the weakness of his army, in 1388 Ivan Sratsimir declared himself vassal to Sultan Murad and allowed the Turks to enter the fortress of Vidin. His aim was to guard his throne and save his subjects from death at the hands of the Turks. For a while he even took Sofia away from the Turnovo kingdom in the hope that, of the three fragments of the Bulgarian state, his would survive. His hopes were soon dashed. The wave of Turkish invasion menacingly approached the borders of his small kingdom. At the beginning of 1396, the European rulers finally realized that the Turkish hordes were a threat to the entire Christian0 world and with the Pope's blessing the Hungarian King Sigismund led a crusade against the Turks. The knights headed southeast, to the Balkans, filling Ivan Sratsimir with hope. He renounced his vassal status, slaughtered the Turkish soldiers in the Vidin fortress and joined the crusaders. However, the Christian army was disunited, each commander seeking personal fame and achievement.

On 25 September 1396 the Turks routed the Christian army at Nikopol. Vidin fell, too. Bulgaria's last medieval ruler was taken captive and died in Asia Minor. Bulgaria fell under a five-century Turkish domination.