In 1803, President Thomas Jefferson agreed to the Louisiana Purchase, successfully adding 530 million acres of land to the United States. The area was purchased from France for $15 million. The following year, President Jefferson assigned Meriwether Lewis (who asked for help from William Clark) to head west and explore the newly purchased land. It took about a year and a half for the duo to reach the west coast.
The War of 1812 resolved outstanding tensions between the United States and Great Britain. The two year war ended British military posts on U.S. soil and British interference with American trade.
The American Civil War divided the United States in two—the Northern States versus the Southern States. The outcome of the four year battle (1861-1865) kept the United States together as one whole nation and ended slavery.