Complex sentence: He joined the army in 1914 as a 2nd lieutenant and reached the status of Colonel by 1920 and, in the same year, served as the Chief of Staff of the state of Michoacán under Lázaro Cárdenas, and became his close friend.
Split into simpler sentences: He joined the army in 1914 as a Second Lieutenant and reached the status of Colonel by 1920. In the same year, he served as the Chief of Staff of the state of Michoacán under Lázaro Cárdenas and became his close friend.