The first military-historical synthesis of the Counts of Celje (Cilli) ['The Counts of Celje (Cilli): History of a Warlike Family'], based on extensive research of primary sources, presents the milestones of their rise to the foremost noble family in the Slovenian lands during the late Middle Ages. Alongside skillful diplomacy and a solid financial foundation, their ascent relied above all on military power. The earlier generations of the Counts of Celje, and the Lords of Žovnek (Sanneck) as their predecessors, successfully exploited military service as a means of strengthening political alliances and expand their wealth. They pursued these ambitions even more confidently in the second quarter of the 15th century, when, at the head of a large private army, they sought to establish an independent principality and secure political dominance in the southeast of the Holy Roman Empire and in the Kingdom of Hungary – even at the cost of open conflict with the Habsburg ruler Frederick V (III), captain general John Hunyadi, and other powerful rivals. In such an unequal struggle, the boldest ambitions of the Counts of Celje ultimately eluded them. In fact, their aspirations to power contributed to the tragic end of the dynasty, which became extinct in November 1456 with the assassination of its last male representative, Ulrich II, in Belgrade. Yet their actions permanently reshaped the history of Europe far beyond their native Celje.