Original sentence: During the eight years of his conductorship Smetana's modern ideas about Czech opera were challenged by other factions within the city's musical establishment.This extended dispute interfered with his creative work, and may have hastened the  health breakdown which precipitated his resignation from the theatre in 1874
Edited sentence: During the eight years of his conductorship Smetana's radical ideas about Czech opera were challenged by conservative factions within the city's musical establishment.This developed into a vendetta against him, which interfered with his creative work and may have hastened the  health breakdown which precipitated his resignation from the theatre in 1874