Final answer:
The increased belief in Manifest Destiny was influenced by technological advancements like the telegraph and the railroad, the annexation of territories such as Texas and Oregon, and cultural and religious rationalizations for American expansion. This belief saw the United States spreading democracy and led to complex domestic and foreign relations issues.
Step-by-step explanation:
During the early to mid 1800s, the increased belief in Manifest Destiny was notably driven by a number of factors. The notion of Manifest Destiny posited that American expansion was inevitable, just, and divinely ordained.
Technological advancements, such as the telegraph and the railroad, played a significant role by improving communication and facilitating travel, which in turn connected the country and helped propel a national market system.
The annexation of Texas and Oregon, as well as the resulting Mexican-American War leading to the acquisition of territories including California, were reflections of this belief.
Manifest Destiny also embedded a cultural and religious justification for expansion, promoting the Americanization of native populations. The concept was deeply intertwined with the national ethos of spreading democracy and certain freedoms "from sea to shining sea."
Furthermore, the era of Manifest Destiny had a profound impact on foreign relations and the internal balance between free and slaveholding states. As the United States acquired more territory, these issues became more complex and contentious.
Support for Manifest Destiny was fueled by both private commercial interests seeking economic opportunities in new territories and a widespread public belief in the nation's exceptional destiny. Senator Thomas Hart Benton, among others, echoed these sentiments, asserting the nation's duty and divine right to expand its borders.