The correct answer is "B".
The Westward expansion started with the Lousiana Purchase in 1803 by the US government to France. It was a period of great demographic and economic growth in the United States. The settlement of vast territories out west offered many migrants from Europe to find a place where they could develop their own wealth and practice their religion without having any oppression. This reality was envisioned by President Jefferson, who executed the Lousiana Purchase, as he believed that a citizen's well being was strongly related to landowning.