Complex sentence: In 1915, he began his major league career with the St. Louis Cardinals and remained with the team for 12 seasons; during this period, Hornsby won his first MVP Award and the Cardinals won the 1926 World Series.
Split into simpler sentences: In 1915, he began his major league career with the St. Louis Cardinals and remained with the team for 12 seasons. During this period, Hornsby won his first MVP Award and the Cardinals won the 1926 World Series.