Because it was getting harder to create new slave-states, so the South was increasingly outvoted in Congress.
There was not one specific date, Westward Expansion happened over a long period of time.
One is the fur trappers
Slavery played a significant role in westward expansion in the United States. The expansion of slavery into new territories and states fueled sectional tensions between the North and South, eventually leading to the American Civil War. The issue of whether new states would allow or prohibit slavery was a major factor in determining the balance of power between the free and slave states, and ultimately the course of westward expansion.
This movement profoundly affected the American character, as it encouraged individual initiative; it made for political and economic democracy; it roughened manners; it broke down conservatism; it bred a spirit of local self-determination coupled with respect for national authority.
Mining for gold and silver brought prospectors and white settlers into many areas including South Dakota, Colorado, Nevada, and California. Because gold was the standard of currency throughout the world economy, gold was essential to keep the country open to trade with European nations. During the Civil War, gold and silver mines were sources of revenue to keep the war going. Later, mining for other commodities like coal, mica, copper, and mercury caused other communities to spring up.
There was not one specific date, Westward Expansion happened over a long period of time.
Because new opportunities and technological advances led to westward migration
One is the fur trappers
Westward expansion led to an economic "boom" in the Midwest, as new cities and markets were connected by rail and canals.
Slavery was a problem that continued to plague the settlers even during the height of the westward expansion and would later be the focus of the Civil War.
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After the Civil War, the US military built the frontier because of the American westward expansion.
Look in the westward expansion after the civil war mini textbook.
Westward expansion created territories that eventually wished to become States. Every application for Statehood prior to the Civil War increased sectional tension because of the need to balance "free" and "slave" States in Congress.
The War of 1812 secured existing US boundaries and defeated tribes in the Ohio and Mississippi valleys. This along with the Indian Removal Act of 1830, opened the door to significant westward expansion by people across America .
The westward expansion in the United States began with the purchase of the Louisiana territory in 1803. The expansion to the west continued until the start of the Civil War in 1861. This period was known as Manifest Destiny.
Fierce debate over which of the new states could be slave-states and which could be free soil.