Much is made of the decline of people doing things with their neighbors. Supposedly this means that American society has become too atomized, or that we're all too busy playing with our shiny electronic doodads to pick our heads up from the screen and enjoy the real world, or other such moral failings. That's bullshit. It sounds good, and it puts the onus on the young to live up to their elders' expectations, which has historically been a pretty good way to motivate people, but it's completely wrong. Americans are interacting with their neighbors less often as a direct result of the places in which more Americans are now living, and the jobs Americans are now working.
Human minds typically seek a balance between social behavior and time alone or with family. Back in the "good old days" of the 1960s and before, work for most Americans involved farming, factory work, hand-written office work, etc. Outside of the high-flyers and creative types like the ones you see in Mad Men, work was typically physical or mental labor, without a lot of need for socialization outside of water cooler banter. This meant that by the time they went home, relaxation and socialization were high on the list of priorities. In the country or the suburbs, kids playing outside and going between houses or into the woods was encouraged. People who lived in cities lived in neighborhoods of people that they felt they could trust, although less so after 1950. The 21st century thus far has flipped that all on its ear.
The media does play a role in the loss of neighborly interaction, but it's that of a scaremonger. Crime was decreasing monotonically from the 1960s up through the Obama administration, when the government decided it was a good idea to encourage race baiting and divisive politics. Part of this was education, part of it was the War on Drugs, and a large part of it was taking lead out of gasoline. Despite this progress, the media has made a habit of over-broadcasting the most horrific crimes nationwide, turning what is statistical background noise into the forefront of people's minds. This drives viewership, but it also makes parents less likely to let their children play outside, even though that's safer than it was back when everybody did it. It is also responsible for the childhood obesity epidemic along with child-targeted advertising and overuse of corn syrup, but that's a thought for another day.
Density of cities is inversely correlated with willingness to hang out with your neighbors. This is most extreme in Tokyo, where sardine like living conditions have produced a culture of hikkikomori who never leave their rooms, and people who will stand on trains packed as full as it is physically possible to be without saying a word to anyone else, but it is noticeable in Chicago and New York as well. Social distance is forced to make up for the lack of physical distance between people. Mexican ~~invasion of the United States~~ illegal immigration has only exacerbated the problem in American cities, since they live two or three times as densely as the number of bedrooms in an apartment would suggest, and being criminals by virtue of being here, are willing to do all sorts of unsavory things so long as "La Migra" (INS and other federal agencies charged with enforcing immigration law) don't notice them.
In the late 20th century up through the housing crash in 2008, forests and fields all over the country were plowed under and turned in to sterile, overly-designed housing developments. This had the dual effect of creating yards unoptimized for outdoor play and removing the wild spaces through which kids once ran. This was done in a grossly space inefficient way to intentionally break lines of sight between neighbors, which commanded a price premium at the time but encouraged the isolationist mentality in the homeowners. I lived in one such neighborhood when I was in high school, and of our whole sprawling complex, I only ever really knew two other families: our next door neighbors, in to whose yard our dog kept escaping, and the family of a teammate and classmate of mine a few blocks away. The iPhone did not hit mass adoption until we had left that neighborhood so I can't speak to the screen-staring bubble's impact on that particular place.
Small cities and towns still encourage neighbors getting to know each other, since there is enough physical space to encourage getting closer socially. In the less than two months I have lived in Bremerton, Washington, I have met all but one of my immediate neighbors, and even had dinner with the ones nearest to me last night. Everyone is relaxed and generally happy with the notable exception of a stereotypical shrieking soccer mom who is generally regarded as the neighborhood's Petunia Dursley. Those types are the same no matter where they live and can generally be disregarded.
So, small towns don't scale to 300 million people, and cities past a certain level of density are harmful to their inhabitants' mental and emotional health. How are we going to handle a growing population?
Spoiler alert: our population would barely be growing at all if not for the unlawful invasion by our southern neighbors. Building a border wall, deporting every single illegal alien at gunpoint if necessary, and repealing the Immigration Act of 1965 would solve density and growth problems as soon as they were fully implemented. Build Planned Parenthoods in every Hispanic urban neighborhood, classify any religion that bans contraception as a public health hazard, and vote for Donald J. Trump for President in 2016, and we can Make America Neighborly Again.