. It was well-known that the term was offensive, even in the 19th century.
Veritas_Certum wrote:
1. When was the word first recognized as offensive?
2. When did this particular offense become unacceptable in broader society?
The answer to the first question is "immediately". Despite apologist claims that this word was not originally intended to be offensive, and that it only became so very gradually over time, there is clear historical evidence that it was always both intended and understood to be a deliberate slur.
The answer to the second question is more complex. It is very clear that many people, even in nineteenth century America, believed the word was so degrading that it should not be used in polite company, or by gentlefolk. However, this took a very long time to percolate throughout the rest of society. Avoidance of the term was a class signifier, demonstrating you were genteel and refined.
Since only a very small proportion of the population originally belonged to this class, it took decade upon decade for the broader public to also acknowledge the term should not be used.
A survey of literature throughout the nineteenth century demonstrates this was widely understood as a deliberately insulting and specifically degrading term, by people who considered themselves among the gentlefolk.
A Christian book published in 1837, describing the treatment of black people in America, identifies the term specifically as "an approbrious term, employed to impose contempt upon them as an inferior race", demonstrating the author was well aware of the meaning and intent of the word. The author (a black Methodist minister and abolitionist), expressed great disgust for the inhumane treatment Africans were receiving and calling on Christians to abolish slavery and improve the condition of African people in the US.
>"Negro, or n\*, is an approbrious term, employed to impose contempt upon them as an inferior race, and also express their deformity of person.", H Easton, A Treatise on the Intellectual Character, and Civil and Political Condition of the Colored People of the United States: And the Prejudice Exercised towards Them : With a Sermon on the Duty of the Church to Them (Boston: I. Knapp, 1837), 40
A historical work published in 1847 explains that it is "an epithet everywhere familiar in the United States", adding that it was a term of degradation and derision. This is important not only because it identifies the usage as widespread in the US, but also because it identifies the term's derogatory meaning as equally widely understood.
>“N\*,” an epithet everywhere familiar in the United States, marked well the degradation which was nursed in derision.", James Schouler, History of the United States of America, under the Constitution. 4. 1831-1847. Democrats and Whigs. 4. 1831-1847. Democrats and Whigs. (New York: Kraus Repr., 1847), 207
A Christian devotional book published in 1848 describes it explicitly as "a term of contempt". Note how the word "negro" is identified as a proper term, whereas n\* is described as a "vulgar nickname".
>"The word "n\*" expresses a common feeling. It is a term of contempt, used by young and old; often thoughtlessly, but not the less is it an indication of the popular feeling. When we call a colored man a negro, we employ a proper distinctive term, implying nothing reproachful or offensive. But "n\*" is a vulgar nickname, always carrying with it something of scorn and insult.", Edwin H. Hawley, Mnemotechny for the Million On the Basis of F. F. Gouraud (Ohio, 1858), 66-67
A book published in 1858, explaining a mnemonic system of remembering facts and improving memory, uses the term in a practice sentence for training the mind, defining it as "a term of contempt which does not become a gentleman in new shows, and a hat". This is important not only because it identifies the word as a deliberate insult, but also because it identifies the word as unfit for a man of good moral character. This shows the author of the book not only understood that the word was a particularly vulgar term, but also that the author considered its usage to be unethical for gentlefolk. This is clear evidence of an objection being raised in the context of class consciousness.
>"N& is a term of contempt which does not become a gentleman in new shoes, and a hat.", Edwin H. Hawley, Mnemotechny for the Million On the Basis of F. F. Gouraud (Ohio, 1858), 34
An autobiography published in 1873 notes the word being used of the people living in India, and describes it as a "term of contempt". This shows not only that the word had become extremely widely used, but that even as its usage was extended to other regions and ethnic groups, it preserved its function as a derogatory expression of contempt.
>"But I was less offended at this, as I noticed that some of them never spoke of the natives of India—who are only dark-skinned Caucassians— except as the “n\*"—the same term of contempt which they have imported to the new world,", Edward Wilmot Blyden, From West Africa to Palestine (T.J. Sawyer, 1873), 76
A volume of the United States Congressional record, published in 1884, describes it as "a vulgar, uneducated way of saying negro", identifying its usage as "contemptuous".
>"I want to ask you if that is not simply a vulgar, uneducated way of saying negro, and if all men who use the term “nigger,” without giving it the proper pronunciation—negro-if all such use it as contemptuous or just from habit?", United States Congressional Serial Set (U.S. Government Printing Office, 1884), 1104
A dictionary published in 1885 describes it explicitly as "A contemptuous or derisive appellation for a negro".
>"A contemptuous or derisive appellation for a negro.", Robert Hunter, The Encyclopaedic Dictionary: A New, Practical and Exhaustive Work of Reference to All the Words in the English Language, ... (Syndicate Publishing Company, 1885), 3288
A book published in 1889 by women's rights activist Elizabeth Stanton, identified the word as "the strongest term of contempt".
>"another example only of the stultifying effect of subjection, upon the mind, exactly paralleled by the Southern slaves, amongst many of whom the strongest term of contempt that could be used was “Free N\*.”, Ida H Harper, Matilda Joslyn Gage, and Susan B Anthony, History of Woman Suffrage (New York, New York: Fowler and Wells, 1881), 93
A book published in 1893, describing life in the Caribbean, identifies the word specifically as an epithet.
>"All sorts of nasty things were said of her, and the most frequent epithet applied to her was “Trinidad n\*.", William Rutherford Hayes Trowbridge, Gossip of the Caribbees. Sketches of Anglo-West-Indian Life. (New York: Tait & Sons, 1893), 140