According to the Anonymous Bulgarian Chronicle, he killed the Wallachian voivode Dan I of Wallachia in September 1386. He also maintained uneasy relations with Ivan Sratsimir, who had broken his last ties with Tarnovo in 1371 and had separated the dioceses of Vidin from the Tarnovo Patriarchate. The two brothers did not cooperate to repel the Ottoman invasion. According to historian Konstantin Jireček, the brothers were engaged in a bitter conflict over Sofia. Ivan Shishman reneged on his vassal obligation to support the Ottomans with troops during their campaigns. Instead, he used every opportunity to participate in Christian coalitions with the Serbs and the Hungarians, provoking massive Ottoman invasions in 1388 and 1393.