It should be taken on a case by case basis. I'm only familiar with circumstances in southeastern North America, but interaction between African slaves and the indigenous populations existed along a whole spectrum of positive and negative occurrences, long and short durations of relationships, and myriad perspectives on those relationships on both sides of the cultural divide. I would argue that only limited development of these sorts of relationships occurred between the establishment of the South Carolina colony (1670) and the Yamasee War (1715). Captured native slaves (often referred to in correspondence as "Settlement Indians") and their African counterparts could interact, but developing more complex relationships was not necessarily possible due to the fear in the colony that this would lead to collusion in revolt, etc. As the colonies expanded and the importation of slaves greatly increased (take a look at the numbers for the Georgia colony from the 1750s up to and through the Revolution, in terms of colonist influx vs slave importation as a proportion of total population) there were still yet restrictions placed on those frontiersmen most often interacting with both slaves and American Indians: deerskin traders. Trade regulations imposed by the Superintendent for Indian Affairs John Stuart limited the number of slaves allowed to be employed by traders in the Indian country and under no circumstances were slaves allowed to venture into tribal lands alone on their masters' business. However, this certainly did not prevent their making their way into the Indian country. I'm not in a position to keep writing much more at the moment and will revisit this later, but suffice to say Indian relationships with their black brethren were often egalitarian to a certain degree (despite being described mythologically by multiple oral histories from the Creeks, Cherokees, and Choctaws as the third formation of man; white clay/red clay/black clay or mud, respectively). Some Creeks and Seminoles (and others, I just happen to be familiar with these) kept slaves themselves, but in many cases the slavery described historically by observers was of an altogether different character. African populations among Indian settlements may have lived separately from the main body or within clan compounds, but were heavily involved in providing for the community at large, participated in community events, and married native women and produced families with children of full status within their mother's clan. A tremendous amount of Creek and Seminole in Alabama, Florida, and on reservations in Oklahoma have African ancestry as they arose from these circumstances. Any resource on the First or Second Seminole Wars and Andrew Jackson's campaigns in the Creek War of 1813-14 will be a decent resource to provide context to those Indian conflicts which involved slave or 'maroon' settlements in the Indian country, and here are some good items to explore: William Ramsay - The Yamasee War Alan Gallay - The Indian Slave Trade Kathryn Holland-Braund - Deerskins and Duffels Robbie Ethridge - Creek Country John Caughey - McGillivray of the Creeks Gary Zeller - African Creeks: Estelvste and the Creek Nation John Mahon - The Second Seminole War Claudio Saunt - A New Order of Things Florida Historical Quarterly - many, search JSTOR Georgia Historical Quarterly - many, search JSTOR John Alden - John Stuart and the Southern Colonial Frontier

I can't speak to the general attitude across the continent, but I wrote a forty page academic paper on race relations in the Cherokee Nation about ten years ago.

The Cherokee adopted race based slavery along with the Creek, to a lesser extent. They also adopted anti-miscegenation laws as to African Americans, with the reversal being the Cherokee was subject to punishment, not the slave. There is a particularly in depth treatment of a prosecuted miscegenation case between a Cherokee man and his black slave in "Red over Black - Slavery Among the Cherokee Indians, by R.Halliburton, Jr. (1977)." I haven't read it in about ten years, so I don't want to get deep into details, but I recall that the Defendant was whipped for sleeping with his slave.

While by no means egalitarian, the Cherokees seemed to have been slightly less abusive and generally looked at slavery as imposing a sort of fiduciary relationship between the parties. There were stories of slaves in Georgia escaping to the Cherokee Nation where they were re-enslaved by the Cherokees, but the general opinion among Southern Whites was that Cherokee slaves were poorly trained, rebellious, and badly behaved. The most memorable anecdote in my studies was of a Georgian who became incensed while passing through the Cherokee Nation when he encountered a Cherokee getting sloppy drunk on whiskey with a slave. The two were sitting up against the barn having a gay old time, passing the bottle between them as equals in total contravention of Southern dining and social custom. The southern white chastised the Cherokee and demanded to be told where the slave's master was so he could be reported. The slave pointed at the drunk Cherokee with whom he was sharing the whiskey.

Ironically, while they took the Cherokee's land, the Federal Government did not take their slaves. Those slaves accompanied the Cherokee to Oklahoma, where the Red-Black slave state was reestablished. The Cherokee Nation sided with the South during the Civil War, and the first non-white general officer in American History was the Confederate Cherokee Chief Stand Watie, who incidentally was the last confederate general to quit the field.

The abolition of the Cherokee Slaves was a rare happy ending, as they were all made Citizens of the Cherokee Nation (Not America), against the wishes of most Cherokee. That entitled them to farm the Cherokee communal land, and in that rare microcosm of the South, freed slaves were able to immediately begin farming for themselves rather than become share croppers.

As far as Assassin's Creed III, my google search indicates the protagonist was half Mohawk, i.e. Iroquois. The Iroquois and Cherokee spoke related languages, but were as separate as Finns and Hungarians by that point in history. A little research shows me the Iroquois had more enlightened views regarding race, but I'll let someone with more expertise on that tribe give a full answer.

Main Source: Red over Black: Black Slavery Among the Cherokee Indians (Contributions in Afro-American and African Studies) by R Halliburton