Writing from a Virginia Indian perspective (Powhatan Paramouncty), I would be interested to hear a more studied answer on this question. I waded through many relevant materials while researching my undergrad history thesis, otherwise consume them in my spare time, and I'm a Virginia Indian active in his community, but I traded history for law (Federal Indian Law). So I defer to flaired users on these matters.

That said, I'm on the lookout for information related to that which OP requested and second OP's request for an answer. My view on the matter is the following:

At the outset of English colonization and even during the latter part of the 17th century, Native American leaders were referred to in more grandiose language. "Emperor Powhatan," "Emperor Opechancanough," "Queen Anne," "King Phillip," et al. are examples of such. Cultural projection is likely.

As the settler-colonist position became more established and Native populations became more marginalized and less useful to Western goals, Western approximations of indigenous titles were also downgraded to "Head Man," "Chief," and the like.

(Personally, I think one of our greatest mistakes was publicly abandoning our own titles, such as Mamanatowick, Weroance, etc.)

The cultural posture and practice metastasized during the gradual period of Western Expansion and the significance of the reduction was likely lost on non-native translators and groups to whom the term was applied. It's doubtful that Native people were completely aware of the framework in which their Western contemporaries were placing them.

I would posit that it goes farther than leadership titles, speaking to a deeper belief in Western cultural supremacy.

For example, you used the term "Tribes" for both Native American and African Nations (my capitalization is admittedly intentional and political).

The general idea and practice in dominating other people is to minimize everything about them except where they pose a threat or where the goal is justifying profitable action against them.

Accordingly:

• "Nations" become reduced to "Tribes" regardless of their structure.
• "Leaders" become reduced to "Chiefs" regardless of their stature or powers.
• "Towns" become reduced to "Villages" regardless of their population.
• Societies that farmed, fished, and hunted become reduced to "hunter-gatherers."

I would be curious as to when the marginalizing language becomes established, then applied on a large-scale. It the Colonial Era there are strong cultural imperialist and supremacist overtones, but I've not noted standardization until sometime after the French and Indian War, but before the Antebellum Period.

Again, I would love to see a sourced answer from one of the regular contributors, even where my observations are refuted. I welcome the reading.

Thank you!

Speaking for the Lushootseed speaking tribes of the Puget Sound, the Chief ("Leader" is a preferred translation for Lushootseed speaking people's) almost always represented his village and that village only. Other villages of the tribe would be autonomously governed by their Leaders and people. The Leaders (occasionally a village might have two) would be used mostly as mediators for any conflict or disputes that might occur in the village, negotiations with other village leaders, when to move sites, and giving feasts. If people didn't agree with the Leader, he couldn't do much about it other than attempt to persuade them to his side.

One Suquamish chief had become rather tyrannical and tried to enforce his will in his village, they responded by killing him outside his home and selected a new chief.