"Facts on the ground" is a common term used in diplomacy to describe a political situation as it exists physically in reality, as opposed to the abstract narratives politicians devise from afar. The mission of settler colonialism is, in essence, to create these so-called "facts on the ground" by moving people to places where a nationality desires more control. History has shown this strategy time and again: the Israeli-Palestinian conflict, the white immigrant populations moving to Texas during the Mexican-American war, Putin's movement of Russians to Crimea. In each case, the power encouraging movement does so in order to increase political sway over that region and to advance the vague diplomatic claim "I want that" to the more persuasive claim of "this is a human rights issue because my citizens live there." From the outset, settler colonialism intends expansion of power through physical occupation.
Economic imperialism, by contrast, remains a little more nebulous. Its mission often begins not with intent to expand territory (as was the case with the East India Trading Company) but to obtain resources from a region. It does so through financial capital, exploitation of the local communities for labor, and the importing of goods obtained. Whereas settler colonialism necessarily displaces or eradicates local populations, economic imperialism leaves the local populations in place and exploits them. This is why, as observed before, places that have experienced economic imperialism are left destitute and unstable, because their means of production and infrastructure have been co-opted.
The effects of these methods can be seen in the years 1750 to 1900 most clearly in the British Empire, though the British were not the sole purveyors. The Dutch were a considerable match for British economic imperialism during this period.
Why it was that Britain chose settler colonialism over economic imperialism in the Americas is perhaps a matter of geography. Whereas in East India and Africa trading routes were already in existence, and the wealth of woven textiles, raw silk, dyes, and opium could be secured through economic means, the distance to the New World demanded that colonies be set in place, local economies erected, and shipping routes established. If Britain was to gain from the riches North America had to offer, it needed its thirteen colonies.
Where the British had seen the vast amounts of wealth accumulated by the French and Spanish during the Age of Discovery, it also saw their decline and sought to follow in their footsteps in the Americas with a more lasting approach. The separation of geography, however, turned out to be a blessing and a curse; it would also contribute to the success of the American Revolution and the subsequent independence of the colonies.
Both settler colonialism and economic imperialism are detrimental to local populations, neither of which can be easily understated. It is sometimes easy to forget the damage caused by settler colonialism when compared to economic imperialism, though, and that is because the latter leaves impoverished populations behind as evidence, whereas the former too often takes the form of genocide.