B. It opened the West to settlement and greatly contributed to the westward movement. This is correct. The Lewis and Clark expedition provided valuable information about the geography, resources, and native peoples of the western United States, which encouraged settlement and spurred the westward movement.
C. It strengthened the Native American tribes against European settlers. This is incorrect, as the Lewis and Clark expedition actually weakened Native American tribes by reducing their bargaining power with European settlers and opening up their lands to further exploration and settlement.
D. It led to the War of 1812. This is incorrect, as the Lewis and Clark expedition occurred before the War of 1812, which took place from 1812 to 1815.
Therefore, the correct answer is B. It opened the West to settlement and greatly contributed to the westward movement.