Weapons are now in existence that are easy for a single person, small faction, or rogue nation to build themselves. Weapons that are capable of striking any group of people on the planet. No one is safe. Worse yet, some of these weapons are capable of annihilating large numbers of people. Worst, some of the biological weapons are uncontrollable and easily built by a basic biochemical lab- these could kill billions of people.
In the next five years, accelerating technological achievements will add vastly more weapons. These weapons also will be usable by small groups to inflict massive global damage.
Our only hope as a species is to unite under one global government. We would be profoundly foolish not to do so.
Bigotry and nationalism will probably prevent this though until massive catastrophes occur. My personal guess is that a small nation like Iran will deploy biological, cyber or robotic weapons against the American populace (since we are the biggest bully on the block). Before that happens, we should open our borders, our trade and our government and encourage the rest of the world to do likewise.