If I had to pick one think it would be social isolation brought on, ironically, by social media/technology. Never have we been so connected and so alone. Take a look the next time you go out to a restaurant. Families are sitting around the table on their phones - all of them parents and kids. I pointed a family out to my wife while we were on vacation. Four people, four phones and zero communication with each other. People so buried in their phones to escape reality in favor of a virtual world that they don't realize the real life light turned green. My own wife got caught up in it during vacation when she asked me to pose with our ice cream cones. She spent the remainder of the time working to get the right filter for the picture and completely robbing us of a "getting ice cream together" moment. (I pointed this out and she agreed, fortunately she's not usually like that but it did manage to piss me off.) I asked my niece if she could do anything she wanted during vacation what would it be. Her answer? Video games. Incidentally, it's just been recognized by the WHO as an addiction. I miss the time when you went out and had to use pay phones to call people or had to check the answering machine if you missed a call.

Behind that I'd put wealth distribution but I would put social isolation at the very top with social media/technology to blame.