In 1803 Louisiana was purchased by Thomas Jefferson. He bought it from France which was led by Napoleon Bonaparte at the time, he sold it because he needed the money for the Great French War.
Texas declared independence from Mexico on March 2, 1836. Terms of the annexation agreement were with Texas retaining all of its public lands and the United States paying $5 million to ease its debts.
The Oregon treaty was signed between the U.S and Britain to settle the boundary dispute. The British gained the land north including the Vancouver Island and the United States received the territory south.