During the Revolution, the Floridas had been returned to Spain. However, by the 1820s, Spain had become weakened, and faced numerous battles with the residents of its empire to the south. Fearing the British might take advantage of this weakness to regain the Floridas, the U.S. convinced Spain to sell the territory. With John Quincy Adams heading up the negotiators, the Adams-Onis Treaty was signed, ceding the Floridas to the United States. This treaty also set out the boundaries between the land obtained in the Louisiana Purchase and the Spanish colony of Mexico to the south. That line followed the Sabine, Red, and Arkansas Rivers, leaving Texas and the Southwest in Spanish possession. Item 154 is a Message from the President...Transmitting a Copy of a Ratified Treaty of Amity, Settlement, and Limits... $1,250.

In 1842, the Webster-Ashburton Treaty set out the border between Canada and the United States in the East. Item 188 is the Treaty Between Her Majesty and the United States... $1,000. However, resolving the western boundary would be more contentious. The cry of "fifty-four forty or fight" would have incorporated much of Canada into the U.S. However, in the year of 1846, America was involved with expansion into Mexican territory, and could not afford confrontation with the British as well. The Americans settled for the 49th parallel, the border today. Item 191 is the Treaty...for the Settlement of the Oregon Boundary. $4,000.

Now the U.S. could focus fully on the Mexican War, and it would be an overwhelming American victory. Texas had already declared its independence from Mexico and been accepted by the U.S. This would be recognized, and what is now the American Southwest and California would be ceded by Mexico. This Treaty of Peace, Friendship, Limits, and Settlement..., better known as the Treaty of Guadalupe Hidalgo, would create the third largest expansion in U.S. history (after Louisiana and Alaska). Item 197. $8,500.

Just one more small piece would be needed to complete the boundaries of the continental states. The southwestern border with Mexico was still farther north at the time than it is today. The U.S. wanted additional land to afford a southern route for a transcontinental railroad. In 1854, land along the southern border of New Mexico and Arizona was purchased for $10 million in what is known as the Gadsden Purchase. Item 202 is a Treaty...United States and Mexico. $225.