Annexing territory refers to the act of acquiring or adding new land or territory to an existing country. In the context of US history, it specifically refers to the acquisition of new territories by the United States.
Related terms
Manifest Destiny: Manifest Destiny was the 19th-century belief that it was America's destiny and duty to expand its borders from coast to coast. It influenced the mindset behind annexing territories.
Anti-Imperialism: Anti-imperialism refers to opposition against expanding a nation's power through colonization or acquiring territories. Those who opposed annexation often held anti-imperialist views.
Mexican-American War: The Mexican-American War (1846-1848) was fought between Mexico and the United States over territorial disputes, including Texas. Opposition to Polk's aggressive stance on annexation arose due to concerns about this war.