Complex sentence: Martin brought the tribe from a 70% unemployment rate in 1997 to less than 3% unemployment in 2007, and during his tenure, led the tribe to become the third largest employer in Mississippi.
Split into simpler sentences: Martin brought the tribe from a 70% unemployment rate in 1997 to less than 3% unemployment in 2007. During his tenure, he led the tribe to become the third largest employer in Mississippi.