When Spain returned Louisiana to France in 1800, one of the stipulations of the Treaty of San Illdefonso was that France would NOT sell the territory to the United States.
The United States purchased the Louisiana Territory from France–more than 800,000 square miles of land stretching from the Mississippi River across the Great Plains to the Rocky Mountains–through a treaty signed April 30, 1803. The Louisiana Purchase doubled the size of the United States at that time.
At 640 acres per square mile, we bought 512 million acres for about $15 million. (Only $11,250,000 was paid directly. The rest was covered by the assumption by the United States of French debts to American citizens.) Less than 3 cents per acre!
The Louisiana Purchase brought the border of the United States adjacent to the border of Texas…and in some places, the claimed territories overlapped. Fuel for disputes!
Teaching Tips: Do the math!