Most of the time when we read the word us, we think about a couple in love or a married couple. . Sometimes we use the word us in reference to our family members.
In biology we learned that a "kingdom" is the first classification of life itself. That got me thinking. How about we use the word us to describe everything that has life on this Earth. Hence the word us can describe Earthlings.
So we are part of an us as Earthlings, part of an us as animal kingdom versus plants, then us as in human beings versus rest of the animals , then us as part of our own family, us as a couple. If we just stick to an us in a limited sense of the word, then other beings from outside the Earth might divide us and take advantage of us.
I would not hold it against anyone if they say that I am thinking like a five year old. The thing is today someone was discussing about their relative who is not recognizing her family members. She apparently said that her HHA (home health aid) was their cousin. I told them that it would not be unusual for an aging person to mix up relatives, then I was told that the HHA was of a different background.