The Louisiana Purchase is the United States’ largest land acquisition. Its story goes back further than Jefferson’s Manifest Destiny. Louisiana and the surrounding territory had been explored originally by Spain and under Spain’s control since 1762. In 1798 Spain disallowed the United States to use the port of New Orleans.
On this day October 1st, in 1800, France secretly attains Louisiana from Spain in the Third Treaty of San Ildefenso. This treaty took place in secret, and was unknown to most of the world until a few years later.
Spain was under economic pressure, defending its colonies from the British and Napoleon. The sale of the land would give them some urgently needed cash. The land sold remained under Spanish control until November 30, 1803 – just three weeks prior to the Louisiana Purchase. The treaty is said to have greatly favored France, and it helped America out as well by doubling its size overnight!