The Iroquois did not have slaves. You might be thinking of individuals that were sometimes taken as compensation for people killed in battle. However, these people were then fully assimilated into the society with all the rights and obligations of anyone in the clan (in most cases, they would even take the name of the deceased). To call these people "slaves" is much more revealing of the Western civilization than that of First Nations.
Did those people have the right to leave or do what they wanted?
https://www.jstor.org/stable/482790?seq=1 Read this paper and the contemporary accounts and tell me that's not slavery.
>To modern Westerners, the use of such a kinship metaphor suggests and is believed to reflect genuine nurturing and closeness; however, in Africa and elsewhere it conveys an entirely different meaning: authority and subordination.
>Villagers, forming a gauntlet and armed with clubs, fire-brands, sticks, and other weapons, greeted the prisoners and rained down on these hapless individuals blows designed to inflict pain but not to kill This was often followed by torture and public humiliation and then deliverance to the grieving families, whose "matrons then chose either to adopt or to execute them," or both
If you look at pages 11-13, there's a discussion of ritual torture to prevent captives from escaping. 13-14 deal with the torture and execution of unruly captives. 15-16 deal with the etymological relationship between "slave" and "pet/livestock" in Iroquonian languages like Mohawk. Pages 17 and 18 discuss people preferring suicide to capture and the sexual exploitation of female captives.