The High Middle Ages were a time when kings, emperors, and popes expanded their powers and created financial and legal bureaucracies to support those powers. Nobles remained the dominant social group, but as monarchs developed new institutions, their kingdoms began to function more like modern states than disorganized territories. Popes made the church more independent of lay control, established the papal curia and a separate system of canon law, approved new religious orders that provided spiritual and social services, and developed new ways of raising revenue. They supported the expansion of Christianity in southern, northern, and eastern Europe and proclaimed a series of Crusades against Muslims to extend still further the boundaries of a Christendom under their control.

Many of the systems of the High Middle Ages expanded in later centuries and are still in existence today. These systems also contained the seeds of future problems, however, because wealthier nations could sustain longer wars, independent popes could abuse their power more easily, and leaders who espoused crusading ideology could justify the enslavement or extermination of whole peoples.