Final answer:
Manifest Destiny was a 19th-century ideology that justified American territorial expansion as inevitable and divinely ordained. It played a critical role in the United States acquiring territories such as Texas, the Oregon Territory, and the lands from the Mexican-American War, including California.
Step-by-step explanation:
Manifest Destiny is a term that expresses the belief that the United States was destined, both by God and by history, to expand its territory and spread democracy and capitalism across the entire North American continent. The ideology of Manifest Destiny played a significant role in the acquisition of various territories of the United States during the 19th century. This expansionist movement justified the annexation of Texas, the Oregon Territory, and was a fundamental cause of the Mexican-American War, which resulted in the United States acquiring vast territories in the Southwest, including California.
The spread of Americanization of Indigenous peoples and Mexican residents, the idea that the physical spreading of the U.S. boundaries equated to the dissemination of freedom, and the intersection of private economic interest with national expansionism were all wrapped in the mantle of Manifest Destiny.
The experience under Manifest Destiny was not uniformly positive; it exacerbated the divisions between free and slaveholding states and troubled relations with other nations like Mexico and the European powers. Despite the controversies, Manifest Destiny was a driving force behind the growth and shaping of the United States during the era of expansionism in the 1840s and beyond.