“Foreignness does not start at the water's edge but at the skin's”
The early registered notions of what later could be identified as ethnocentrism come from the first scientific stages of interests about Darwinist ideas (1879) noticing that competition between groups who perceive themselves as different from the others increased their inner group cooperation and later (1892) Spencer addressed that the behavior inside the members of the group perceived as similar to us is different than the narrative towards groups who are perceived different from us.
Later, in the early 1900s, Mcgee uses the term in a less biological and more social way indicating that ethnocentrism is similar to egocentrism but applied to groups. “Knowing little of the external world, tribesmen erect themselves or their groups into centers about which all other things revolve” (Mcgee pp. 830–831 on Bizumic & Duckitt, 2012)
Evolutionists of those days was added by comparing embryonal stages with cultural blossom basically to justify the invasions who had as a goal, the appropriation of material wealth. Under the idea that “those others different from us are barbarians, savages”
Some authors recall that the term Ethnocentrism raised more notoriety when Sumner (1911) defined it as “The sentiment of cohesion, internal comradeship, and devotion to the in-group, which carries with it a sense of superiority to any out-group and readiness to defend the interests of the in-group against the out-group, is technically known as ethnocentrism”
When "us" feels not only different but also better
Here and with the addition of that uncomfortable truth related to the self-perception of our group as superior or better than others, that happen to be just different is that the term “ethnocentrism” was going to be used in analysis by psychology, political science, sociology, and economics as much as in anthropology.
The most important addition by Levine and Campbell (1972) was the observation that with ethnocentrism a person’s values are applied in the perception of other groups. The person acknowledges its own values as better or superior from other sets of values, like more “moral”, “correct”. Thought by itself is not that bad and has a limited field of action until it is shared and it becomes “the truth”.
A story about early ethnocentric (intentions)
Ethnocentrism can be built from the view of the dominant, colonialist culture and under that perception, the "dominant culture" is the one that does the writing and settles the POV. Practices like ethnography, can help to give a voice to the non dominant cultures but still treating them as “different from us” and also inferior in some cases.
Writings about the interaction between civilizations have left precious testimony about those days when the assumptions of these “comfortable truths” about ourselves-different-from-those-other-groups still had limits.
In this case, is the offer that the Virginia Government made to the Six Nations, which consisted in giving "education" to a group of young Native Americans (Iroquois) in their new University settled in Williamsburg. The following quote is an extract of the answer the Six Nations gave, event registered by Benjamin Franklin in 1774:
"We are convinced therefore that you mean to do us good by your proposal, and we thank you heartily. But you who are wise must know, that different nations have different conceptions of things; and you will therefore not take it amiss if our ideas of this kind of education happen not to be the same as yours. We have had some experience of it: several of our young people were formerly brought up at the colleges of the Northern Provinces; they were instructed in all your Sciences; but when they came back to us they were bad Runners, ignorant of every means of living in the woods, unable to bear either cold or hunger, knew neither how to build a cabin, take a deer, or kill an enemy, spoke our language imperfectly; were therefore neither fit for hunters, warriors, or counselors; they were totally good for nothing. We are however not the less obliged by your kind offer, tho’ we decline accepting it, and to show our grateful sense of it, if the gentlemen of Virginia will send us a dozen of their sons, we will take great care of their education, instruct them in all we know, and make men of them.”
The previous quote shows how the people who were making "the invitation" saw their education as universal and necessary for those ones who were different without considering that different cultures and circumstances might need different skillsets, that progress could only happen in that way.
The cultural colonization projects have a strong ethnocentric load, the practices, knowledge, and experience of the ones who drive it and consider themselves positive or special among the rest. Nowadays the economically and politically predominant cultures no matter the source of their richness, create a culture in the now globalized nations about how it “should be” and not always in an explicit way, but the rules settled there, are the ones other nations aspire to. “On the observed long term, it can help to deeply divide societies, and be very hard to remove from mentality, and cultural expressions” (M.C. Chiriguini & Mariana Mancusi, 2008)
It is possible to think that the skills valued in one culture, are not necessarily shared by the other ones, and there is nothing bad about it, but the raising and radicalization of certain ideas of superiority aligned with colonization and other social factors can lead to a colonizer-oppressed long term dynamic.
That is the breaking point when the identification of "us" different from "others" breaks into "us" being better than the "others". Ethnocentrism can always lead to passive thoughts of mild perceptions, another expression of it has been noticed in consuming patterns ¿ehat do we chose to buy everytime? Based on what? Does it have a relationship with the place that product came from? Are we sure that certain country makes the best cheese? Why?. But when this blind choices are applied to political decitions it turns into deeper and way mor regrettable practices.
It did not happened to indigenous people from the whole of America, it still happens today when a stereotype is created, stereotypes can easily be a child of ethnocentrism. Stereotypes stops our curiosity and our ability to open our minds, or find out by ourselves.
It can happen easily when people from certain areas of the world think that the other ones know less or deserve worse just because it is inconceivable that those others different and “probably inferior” become relevant. It can happen on a short interaction while traveling or on a massive political conflict. Ethnocentrism is dangerous, but talking about it, identifying the real reasons under the way we label others and their features can help not to make it grow worse. It is hard to not have some of it, being that it is acquired from previous generations, is that why it can always dangerously rise again.
 Benjamin Franklin about Native Americans (1774) in Adams 1966
Aguilera Portales, R. (2002). El problema del etnocentrismo en el debate antropológico entre Clifford - Geertz, Richard Rorty y Lévi-Strauss. Gazeta de Antropología. https://doi.org/10.30827/Digibug.7399
Bizumic, B., & Duckitt, J. (2012). What Is and Is Not Ethnocentrism? A Conceptual Analysis and Political Implications: What Is and Is Not Ethnocentrism? Political Psychology, 33(6), 887-909. https://doi.org/10.1111/j.1467-9221.2012.00907.x
Durá, N. S. (2013). Actualidad del relativismo cultural. Desacatos. Revista de Ciencias Sociales, 41. https://doi.org/10.29340/41.84
Hales, D., & Edmonds, B. (2019). Intragenerational Cultural Evolution and Ethnocentrism. Journal of Conflict Resolution, 63(5), 1283-1309. https://doi.org/10.1177/0022002718780481
M.C. Chiriguini & Mariana Mancusi. (2008). Apertura a la Antropología: Alteridad, cultura, naturaleza humana. Buenos Aires: Proyecto Editorial.
Sutherland, L. L. (2002). Ethnocentrism in a Pluralistic Society: A Concept Analysis. Journal of Transcultural Nursing, 13(4), 274-281. https://doi.org/10.1177/104365902236701