Original sentence: But the period of revival was interrupted when the city was plunged into internal strife by the 13th-century struggle between the Ghibellines, supporters of the German emperor, and the pro-Papal Guelphs after the murder of nobleman Buondelmonte del Buondelmonti for reneging on his agreement to marry one of the daughters of the Amidei family
Edited sentence: But the period of revival was tragically interrupted when the city was plunged into internal strife by the 13th-century struggle between the Ghibellines, supporters of the German emperor, and the pro-Papal Guelphs after the murder of nobleman Buondelmonte del Buondelmonti for reneging on his agreement to marry one of the daughters of the Amidei family