American Expansion refers to the period in the 19th century when the United States grew its territory significantly. This expansion was driven by the belief in Manifest Destiny, the idea that Americans were destined to spread across the continent. Key events included the acquisition of territories through treaties, purchases, and conflicts, such as the Louisiana Purchase and the Mexican-American War. During this time, settlers moved westward, seeking new opportunities and land. The expansion often led to the displacement of Native American tribes, as their lands were taken for settlement and development. This period shaped the nation's borders and influenced its cultural and political landscape.