Complex sentence: At the time of John W. Carter's death, his son, Richard B. Carter was still studying at Harvard, but after his graduation in 1898, he joined the company and after a period of learning the business became its head in 1903.
Split into simpler sentences: At the time of John W. Carter's death, his son, Richard B. Carter was still studying at Harvard, but after his graduation in 1898, he joined the company. After a period of learning the business, he became its head in 1903.