Complex sentence: The first permanent fort established in Montana was Fort Benton, established as a fur trading post in 1847 and upon being purchased by the US Army in 1865 was named in honor of Senator Thomas Hart Benton, who encouraged settlement of the west.
Split into simpler sentences: The first permanent fort established in Montana was Fort Benton, established as a fur trading post in 1847. After it was purchased by the US Army in 1865, it was named in honor of Senator Thomas Hart Benton, who encouraged settlement of the West.