Complex sentence: He was Director of Army Plans from 1990 to 1992, then commanded the 1st Regiment the Royal Horse Artillery from 1992 to 1995 and saw service in Bosnia in 1995--1996, before taking a Higher Command and Staff Course in 1997.
Split into simpler sentences: He was Director of Army Plans from 1990 to 1992, then commanded the 1st Regiment the Royal Horse Artillery from 1992 to 1995. He saw service in Bosnia in 1995 to 1996, before taking the Higher Command and Staff Course in 1997.