From Wikipedia:
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The phrase itself, and the underlying belief of interconnectedness with all creation, is a part of many Yankton Sioux prayers,and is found in use among Lakota, Dakota and Nakota people.
Translations and themes
The phrase translates as “all my relatives,” “we are all related,” or “all my relations.” It is a prayer of oneness and harmony with all forms of life: other people, animals, birds, insects, trees and plants, and even rocks, rivers, mountains and valleys.