Final answer:
Early settlers spread across the Americas due to economic opportunities, religious freedom, and the ideology of Manifest Destiny, leading to clashes with and displacement of indigenous peoples and significant cultural changes.
Step-by-step explanation:
The main reason that early settlers gradually spread across the Americas was multifaceted, including the pursuit of economic opportunities, the desire for religious freedom, and the philosophical ideal of Manifest Destiny. Settlers were driven by the promise of rich land for farming, ranching, and mining, while others sought to escape the confines of their homeland in search of religious expression or to spread their faith. Additionally, the belief in Manifest Destiny encouraged the notion that Euro-American settlers were predestined to expand their culture and technology across the continent. This movement led to significant changes in social structures, economies, and interactions with indigenous populations.
European immigrants, particularly from Northern Europe, sought out new lives in ethnic enclaves for comfort and familiarity, while African Americans fled the racism of the South. The westward expansion was not just about the American Dream of a better life; it significantly affected native populations through warfare, disease, and cultural conflicts, and introduced a new way of life that was often at odds with the existing Indigenous cultures.