Complex sentence: He earned a Mention in Despatches in May 1992, before promotion to lieutenant colonel in 1995, colonel in 1999 and brigadier on 31 December 2001, with seniority from 30 June 2001.
Split into simpler sentences: He earned a Mention in Despatches in May 1992, before promotion to lieutenant colonel in 1995. He was colonel in 1999 and brigadier on 31 December 2001, with seniority from 30 June 2001.