Complex sentence: Carlsen was signed by the Cubs as an amateur free agent in 1944 at age 17, and worked his way through the minor leagues until he got promoted to the Cubs in 1948.
Split into simpler sentences: Carlsen was signed by the Cubs as an amateur free agent in 1944 at age 17. Afterward, he worked his way through the minor leagues until he got promoted to the Cubs in 1948.