Originating in the 19th century, Manifest Destiny was a belief that the US was destined to spread throughout the American continents. That this spread was inevitable and therefore justified, at any cost. The idea was that manifesting this inescapable advancement was the duty of all US citizens of the time.
The term was originally coined in a rhetorical manner, featured in an article titled Annexation. The underlying themes of Manifest Destiny, that America and its settlers had a duty to spread industrialism west, carried along with them the fact that to see this mission to its end, slavery would need to continue and even be expanded.
There were many critics of the idea, many claiming that those who utilized this idea only did so in seeking justification for activities only based in discrimination and selfishness. Regardless, the term was employed by Democrats to defend the war against Mexico and the splitting of Oregon with the British, as well as the push to eradicate Native power and expand slavery.
In fact, this overwhelming urge on the part of some to push west and bring enlightenment to the savages that occupied the land there came at a great cost, both to early US citizens and to the Native American and slave populations.
Despite political dissension surrounding the main themes of Manifest Destiny, the US government continued pushing west, removing Native American populations from their own lands, inciting skirmishes and wars with them. Those that supported Manifest Destiny believed that Native Americans were better off living separately from ‘whites’ and that the Native way of life would simply fade away.
The Homestead Act of 1862 was another attempt at forcing the expansion of America, going hand-in-hand with the removal of Native peoples from their traditional lands. Offering free land, usually around 160 acres, to almost 600,000 families, the only requirement was to stay and improve the land for 5 years.
While the idea was popular with pre-civil war Democrats, it was a highly contested school of thought, even among some notable American figures including Ulysses S. Grant and Abraham Lincoln. John Quincy Adams, who originally had been a great supporter of Manifest Destiny, rejected the continuation of slavery in 1843.
By the turn of the 20th century, during the presidency of Teddy Roosevelt, Manifest Destiny had fallen from grace. Both the term and the forced expansion west had come under so much fire from opponents that it was no longer seen as healthy for the growing nation. Roosevelt and his successor Woodrow Wilson both explicitly rejected expansionism in favor of interventionism and the idea that the world should be a safe haven for democracy.