Complex sentence: Anton Armstrong became only the 4th director of the St. Olaf Choir in 1990, continuing the tradition begun by the choir's founder F. Melius Christiansen in 1911.
Split into simpler sentences: Anton Armstrong became only the 4th director of the St. Olaf Choir in 1990. He continues the tradition started by the choir founder F. Melius Christiansen in 1911.