I think we may be experiencing the adverse effects of the Information Age coupled with the digital revolution. In the previous generations (pre-TV, pre-Internet, pre-24 hour news cycles, pre-portable e-devices) I think there were just as many natural disasters, tragic deaths from famine/disease/war, poverty, plagues, and such - there just was not as much news coverage of all of it.
I understand we are ruining our environment, our globally-connected financial exchanges, machines that make killing more efficient, food and medicine shortages, genocide and tribal wars are occurring, and emerging countries are developing nuclear weapons. But I have to say, I have seen a lot of such things in my life, and sometimes it was worse. I grew up in the Vietnam, Watergate, multiple assassination era of the late Sixties and I recall things then that are honestly worse than what we are seeing now.
I think our society has become more "dark" in its culture. Our movies and entertainment are more violent and celebrate horror as a way to create excitement. Look at the movies that are drawing big crowds - half of them are horror flicks or focus on the evil side of human existence. America has always been a violent society - we won our freedom and conquered our Country's land using guns - this is an undeniable part if our history. But I think a lot of the "gloom and doom" comes from how our media spins things ("if it bleeds, it leads" - "we love dirty laundry") and I think that impacts people's psyches more than we realize, and more than is called for.
I have friends who never watch the news, don't follow politics or register to vote, don't use e-mail or the Internet, and although I find them somewhat uninformed and not very sophisticated, they all are happier than the fast-lane frequent-flyer caffeine-addicted business-world people I work with. They do not have near the same level of anxiety, because they choose not to watch or read things that keep them awake at night. They are all not as financially successful as they could be if they were more "driven" but I bet they will outlive me. They just have a lower tolerance for stress, I believe, or so it seems. But they smile and laugh a lot more, too.
I am just saying a lot of this talk about the decline of America is premature. We have seen more difficult days (the Great Depression, World War II and the rise of fascism and totalitarianism) and we are still here, and people all over the world still want to come here and aspire to be like us. We are still the most powerful and richest country on Earth, and I don't see that changing in the next 20 years.
For all that is wrong with the world, we are still living in the best Country there is, in so many ways. We will overcome the setbacks. It's what we do.