Though I'm not a big Wikipedia quoter, here's what it's got on the historical use for anyone confused about how offensive the term may be:
"Redskin" was used throughout the English-speaking world (and in equivalent transliterations in Europe) throughout the eighteenth and nineteenth centuries as a common term of reference for indigenous Americans. However, the more commonly used term from early colonization through the twentieth century was "Indian", perpetuating Columbus' belief that he had found the Indies.[9] The first use of red-skin or red Indian may have been limited to specific groups that used red pigments to decorate their bodies, such as the Beothuk people of Newfoundland who painted their bodies with red ochre.[10] Redskin is first recorded in the late 17th century and was applied to the Algonquian peoples generally, but specifically to the Delaware (who lived in what is now southern New York State and New York City, New Jersey, and eastern Pennsylvania). Redskin referred not to the natural skin color of the Delaware, but to their use of vermilion face paint and body paint.[11] The indigenous peoples of the continent had no common identity, and referred to themselves using individual tribal names, which is also preferred to the present day. Group identity for Native Americans only emerged during the late 18th and early 19th century, in the context of negotiations between many tribes signing a single treaty with the United States.[12]
Some claim the term is a particularly egregious racial epithet that represents a bloody era in American history in which Indigenous Americans were hunted, killed, and forcibly removed from their lands by European settlers.[13] The claim often centers around a proclamation against Penobscot Indians in 1755 issued by King George II of Great Britain, known commonly as the Phips Proclamation.[14][15] The proclamation orders, “His Majesty’s subjects to Embrace all opportunities of pursuing, captivating, killing and Destroying all and every of the aforesaid Indians.” The colonial government paid 50 pounds for scalps of males over 12 years, 25 pounds for scalps of women over 12, and 20 pounds for scalps of boys and girls under 12. Twenty-five British pounds sterling in 1755, worth around $9,000 today —a small fortune in those days when an English teacher earned 60 pounds a year.[14] However, since the proclamation itself does not use the word redskin, citing it as the origin of "redskin = scalp" has also been called "revisionist history".[16]
A linguistic analysis of books published between 1875 and 1930 show an increasingly negative context in the use of redskin, often in association with "dirty", "lying", etc.; while benign or positive usage such as "noble" redskin were used in a condescending manner.[9] The term continued in common use until the 1960s, as evidenced in Western movies, but is now largely considered a pejorative and is seldom used publicly (aside from the football team - see below). As with any term perceived to be discriminatory, different individuals may hold differing opinions of the term's appropriateness.[17]
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Now regardless of whether the term Redskin was used in the Phips proclamation or not, if a group of people with the orders to exterminate another group, devise a nickname for that group, then yes, that nickname will be deemed racist. It's not even a question.