Americans are mean to each other. We didn’t used to be. Various explanations exist. Isolation like many behaviors can be thought of as a defense mechanism, a reaction. Solutions are obvious. What made us different in the past?
A political identity based on belligerence, narcissism, and toxic individualism, has taken root and replaced religion for a great many people. Not that religion was all that great, but the current "everyone for themselves and fuck anyone who is not like me" movement is a hell of a lot worse. For these people, isolation is not a defense mechanism, it's a core value. They're against anything that diminishes the Individual, like collective action and cooperating for the good of society.
Social conformity enforced through rigid Christian indoctrination, centralized media propaganda and racial segregation. It's easy to be nice to each other when everyone around you looks like you do, thinks like you do and agrees with your politics.
The breakdown of American social cohesion can be traced to at least three related factors - the deconstruction of white supremacy due to the increase in political and cultural power of people outside the white, heteronormative Christian conservative complex, the internet decentralizing mainstream, corporate controlled media as a means of propagandizing and reinforcing the consensus narrative of American exceptionalism, and late capitalism destroying a lot of consumer social interaction like going to the movies, dance halls, etc - because many people no longer have the time or money to engage in physical interaction with other people outside of the workplace, whereas the internet offers forms of interaction that are relatively free.
