Which idea is encapsulated in the concept of "Manifest Destiny"?

The concept of "Manifest Destiny" fundamentally revolves around the belief that American expansion across the North American continent was both justified and inevitable. This idea emerged in the mid-19th century and was fueled by a sense of mission among Americans, who viewed it as their divine right to expand their territory and influence. Proponents believed that it was America's destiny to spread its democratic values and institutions across the continent, which they often equated with progress and civilization. This belief played a significant role in events such as the westward expansion, the annexation of Texas, and the Oregon Trail, ultimately contributing to significant territorial acquisitions, including areas gained through the Mexican-American War.

The other choices do not capture the central theme of Manifest Destiny. The notion of isolationism runs counter to the idea of expansion; equal rights for all is not specifically linked to territorial expansion but rather focuses on social justice; and while the spread of American culture may have been a byproduct of expansion, it does not encompass the core idea of inevitability and justification inherent in Manifest Destiny.