Jump to: Background Suggestions for Teachers Additional Resources Background In 1803, the United States doubled in size at the stroke of a pen. The Louisiana Purchase Treaty, which was signed in April of that year and ratified by the Senate in October, transferred hundreds of millions of acres of land west of the Mississippi River from France to the U.S. for a few cents per acre. This acquisition opened up new opportunities for westward expansion by the U.S. It also began a period of dramatic tr