Final answer:
After 1776, American settlers expanded westward, driven by land speculation, economic opportunity, and soil exhaustion from tobacco farming. This migration often resulted in conflicts with Native American tribes and was further fueled by social, economic, and political factors that created a significant demographic shift in the U.S.
Step-by-step explanation:
The post-1776 expansion of American settlers in the eastern part of the 13 colonies was driven largely by land speculation and the pursuit of economic opportunities. Settlers traversed the Appalachian Mountains to stake claims, drawn by the allure of fertile soils in the Ohio Valley and beyond. This westward movement often led to conflict with Native American tribes who resisted further intrusion onto their lands. The expansion was also influenced by a desire to diversify holdings beyond tobacco farming in Virginia, which had led to soil exhaustion. The British government, concerned about further antagonizing Native American tribes and maintaining control over the increasingly independent-minded colonies, restricted settlement west of the Appalachians, which was met with disdain by the colonists.
The concept of Manifest Destiny did not originate in the 1840s but had roots in the early expansionist desires of the American settlers. Despite the British victory over the French in the colonial wars, colonists were dismayed when the British prohibited them from settling lands they expected would be open to them following the Peace of Paris.
Ultimately, the push westward was a complex mix of social, economic, and political factors that led to a significant demographic shift by the mid-19th century, with nearly half of all Americans living west of the Appalachian Mountains. This quest for more land continually reshaped the American frontier and fueled the growth of the United States.