3. Why is Simeon's reign often called as Golden Age of Bulgaria? During Simeon's reign, the country expanded. We usually call someone greatest leader to who expanded country the most. More land, better/stronger country. It has been like fundamental of that time period 4. What do Bulgarians commemorate on their National Liberation Day? It commemorates the Liberation of Bulgaria during the events of the Russo-Turkish War that led to the re-establishment of a Bulgarian statehood. ... It was officially designated as Liberation Day on its 10th anniversary in 1888 by the Principality of Bulgaria.