Complex sentence: This, in turn, led to aspirations for more self-rule among the most influential nobles who established semi-independent fiefdoms that nominally recognized the emperor in Tarnovo and greatly reduced the capacity of the central authorities to deal with the external threats.
Split into simpler sentences: This, in turn, led to aspirations for more self-rule among the most influential nobles. Many of them established semi-independent fiefdoms that nominally recognized the emperor in Tarnovo and greatly reduced the capacity of the central authorities to deal with external threats.