The U.S. acquires a vast territory from France, setting the stage for further westward expansion.

The U.S. engages in a war with Mexico, resulting in the Treaty of Guadalupe Hidalgo and the acquisition of a significant amount of land, including present-day California, Nevada, Utah, Arizona, New Mexico, Texas, and parts of Colorado, Kansas, Oklahoma, and Wyoming.

The treaty ends the Mexican-American War and adds over 500,000 square miles of land to the United States, fulfilling the concept of Manifest Destiny.

The first transcontinental railroad is completed, connecting the East and West coasts of the United States and facilitating further expansion and settlement.