What can you tell me about the westward expansion during 1820-1850?

The westward expansion of the US between 1820 and 1850 represented what was considered America's manifest destiny to control the North American landmass from the Atlantic to the Pacific Ocean. President Thomas Jefferson completed the Louisiana Purchase to provide land for what he hoped would be a wave of small farmers spreading republicanism far and wide. The West also represented freedom to the millions of immigrants coming from Western Europe, who had left behind lives of poverty in their newly-industrialized nations and yearned for wide-open landscapes where they could farm and do as they pleased. Pioneers survived hardships and months of arduous travel to settle the lands that Jefferson bought and Lewis and Clark surveyed.
During the expansion, the United States butted heads with Great Britain over the Oregon Territory and with Mexico over California, Texas, and territories that now form the US Southwest. The United States almost came to blows with Britain before settling its differences with an 1846 treaty, and it did come to blows with Mexico, which was still smarting after losing Texas in 1845. The US won the Mexican War in short order and extracted territorial concessions that included more than one million square miles of land. A few years later, the Gadsden Purchase allowed the US to build a southern railroad line and marked the last land addition to the contiguous forty-eight-state region.
One final point about westward expansion—the new states formed from the lands purchased from France and gained from Great Britain and Mexico helped exacerbate the slavery arguments that eventually led to the US Civil War. Southern states realized that as more free states were formed from western territory, they would soon be in such minority status in Congress that they would be unable to stop the passage of anti-slavery legislation. This led to the Missouri Compromise of 1820 and other stopgap measures that only delayed the inevitable fight that would be needed to end slavery in the United States.
http://www.theusaonline.com/history/expansion.htm

https://www.history.com/topics/westward-expansion