When looking at the ideas that scientists, especially biologists, had about species and races, especially concerning humans, in the 1700's and 1800's, much of it sounds quite horrible to our modern more knowledgeable ears.
Back in those times there was a great deal of discussion in science about the question of how many species/races (the difference between the two concepts seems to be a bit fuzzy back in those days, often up to the point of the two terms being used interchangeably) of humans there are, and what their biological relation is to each other. Much of it sounds really, really degrading and blatantly racist to our modern sensibilities.
The prevalent view back in those days was that all living beings could be categorized in terms of development. In other words, some species were more developed and others less developed. All species could be put in a "ladder" according to how developed they were. Worms were pretty down low in this ladder, dogs a lot higher, and humans obviously at the very top. Apes were (also rather "obviously") slightly lower in the ladder.
Back in those days scientists did not have the tools and knowledge that we take for granted today. They didn't have any idea of DNA, or how to compare species with each other using it. Likewise there was basically no notion of speciation, and the origin of species was pretty much an open question (often just attributed to divine creation even in the case of the most secular of scientists).
The only things they had to work with was morphology and behavior. And this is, perhaps, the crux of the whole question. When they observed primitive tribes of humans, they only had morphology and behavior to work with, when the question came up whether they are humans, apes, or something in between. Based on their primitive behavior, many scientists did classify them as entirely separate species/races somewhere in between apes and humans in the "ladder".
About the question of how many species/races of human-like living beings there were, estimations ranged all the way from 3 to over 60, depending on the author.
Obviously white people were almost universally considered the highest step on the "ladder", and all of the other species/races to be lower.
As said, this sounds quite obnoxiously racist to our modern sensibilities. However, should we judge them so harshly? I'm not saying there was no sentiment of superiority in one degree or another, but regardless, we should understand what were the tools they had to work with. As said, they didn't even know of DNA, or inheritance, or anything like that, and the only thing they had to work with was morphology and behavior. Lacking any better knowledge, they classified people as lower or higher based in their cultural development, rather than their genetic material (which they didn't know about.) We of course now know that this is the wrong tool to use, but they didn't know that back then.
So, once again, should we judge them so harshly? I'd say no. We should give them the benefit of the doubt. While there was certainly some elitism among many of them, I'm certain that many of them classified humans into species/races with no ill will, purely based on their observations and their (limited) knowledge.
Charles Darwin was, in fact, surprisingly progressive in this regard. He, in fact, in his books criticizes all those scientists, posits that there is no "ladder" (and proposing an evolutionary tree with all the branches, representing all extant species, being at the same level), and posits that all humans are in fact the same species (ie. one single branch of the tree).
Creationists often accuse Darwin of having been a racist. This is a complete fabrication. In reality it was the exact opposite: Darwin was in fact one of the least racist scientists of the time, and in fact proposed that all humans are actually the same species and biologically completely equal to each other, and heavily criticized contemporary science for classifying some humans as inferior. His hypothesis was rather bold and controversial at the time, but later knowledge (especially thanks to the discovery of DNA and DNA testing) proved him absolutely right.