Based on the context of the Louisiana Purchase and its impacts, the most accurate inference among the statements provided is:
Because of the purchase of the territory, Americans could now legally start settling regions in the West.
This statement reflects the effect of the Louisiana Purchase on westward expansion, as it significantly increased the territory of the United States and opened new lands for settlement. The other statements may have some validity, but the strongest inference directly related to the effects of the purchase and its implications for expansion is the one regarding settlement in the West.