American Expansionism refers to the 19th-century policy of the United States to extend its territory across North America. This movement was driven by the belief in Manifest Destiny, the idea that Americans were destined to expand their land and influence. Key events included the acquisition of territories through treaties, purchases, and conflicts, such as the Louisiana Purchase and the annexation of Texas. The expansionist period also involved the displacement of Native American tribes and conflicts with other nations, including the Mexican-American War. This era significantly shaped the geographical and political landscape of the United States, leading to its emergence as a continental power.