Complex sentence: During his career in the House of Representatives, Floyd was an advocate of settling the Oregon Territory, unsuccessfully arguing on its behalf from 1820 until he left Congress in 1829; the area did not become a territory of the United States until 1848.
Split into simpler sentences: During his career in the House of Representatives, Floyd was an advocate of settling the Oregon Territory, unsuccessfully arguing on its behalf from 1820 until he left Congress in 1829. The area would not become a territory of the United States until 1848.