Complex sentence: Harmanli Massacre refers to the massacre of Muslims in Harmanli by Russian troops in 1878, The Congress of Berlin and after, William Norton Medlicott, page 157 during the Russo-Turkish War (1877--1878).
Split into simpler sentences: Harmanli massacre refers to the massacre of Muslims in Harmanli by Russian troops in 1878. During the Russo-Turkish War (1877--1878).