It's even simpler than that. Due to our evolution (we were hunter gathers of eighty or ninety percent of our species existence) we have some built in hardwiring. Dunbar's number is an example

"we" can only hold so many people in our minds as real. Generally speaking that number is a hundred (or so) That hundred are "us". When that number is exceeded they are "them".

In other words family, clan and tribe.
Beyond the tribe it all breaks down.
Insane in other words.
A chaotic system.
Chaos has no rules.