Complex sentence: They were a weak team in their early years, but started to improve in 1891, two years after moving to the National League thanks in large part to their signing future Baseball Hall of Fame pitcher Cy Young.
Split into simpler sentences: They were a weak team in their early years, but started to improve in 1891, two years after moving to the National League. This improvement was largely due to the signing of future Baseball Hall of Fame pitcher Cy Young.