Complex sentence: Between 1839 and 1840, Sibley served as president of the Missouri Internal Improvements Board and as a railroad commissioner, and in 1844, he ran for a seat in the Missouri Senate, but lost.
Split into simpler sentences: Between 1839 and 1840, Sibley served as President of the Missouri Internal Improvements Board and as a railroad commissioner. And in 1844, he ran for a seat in the Missouri Senate but lost.