We versus Them

If you had seen the youtube of Dr Hans Rosling, you would have heard of this before.

There is often this distinction between us and them. In the Dr's case, he was teaching global health, and his students seemed to divide the world into WE vs THEM.

WE = Westerm (developed) world
THEM = Third world countries

Why is there distinction of this sort? We are all humans, and just because they were born in a less developed country does not make them any less.

Humans seem to have this innate need to divide and categorise. Why is that the case?
To feed our ego into thinking that we are always better?
But while conditions and circumstances are different, fundamentals are the same.
We all have a human body that will grow old, sick and die.

Your body will become ashes or rot when you die. There is no difference in that.
So why them vs us? It doesnt make any sense to me.

While I say all that, I do realise and admit that the old mindset of distinction is not an easy one to rid.
Let's all work together to have equality and equanimity for ALL. [including animals, etc]