The question of what went wrong in the world is complicated, since a great many different things went wrong, however, I will give you a very simplified summary. Bear in mind that I am necessarily leaving out a lot of details.
Every mistake collectively made by the human race has long-term consequences. For example, people have been burning fossil fuels for a long time. The amount burned per year has been increasing since the beginning of the Industrial Revolution. The carbon dioxide content of the atmosphere has been rising for centuries. It has now gotten to a level at which it is affecting the global climate. This is causing some serious problems - and those problems have really just begun. If you think that the year 2016 is fucked up, just wait.
Most of the world's current political problems can be traced back at least as far as WW I. For example, the middle east used to be governed by the Ottoman Empire and as a result it was politically stable for about 500 years, but the Ottoman Empire backed the wrong side in WW I and was dismantled. Since then, many other mistakes were made by European colonial powers which made the region progressively less stable. Now it's a mess. And that mess is spilling over into the rest of the world. It is very hard to contain.
The global population has been steadily increasing for centuries. It has approximately doubled just in the past 50 years or so - quite a rapid rate of increase. This creates pressure on all areas of resource consumption, carbon footprint etc. Planet Earth does not get larger to accommodate the increased population. It just gets more crowded. There is conflict over scarce resources. This conflict can only increase.
During the Cold War era (1945 - 1990) the US was mainly concerned with containing international communism, and it supported (or placed into power) many deeply corrupt anti-communist dictatorships such as that of Shah Pahlavi of Iran. The US is immensely resented in most of the world, as a result.
Many nations including the US have found it easier to borrow money than to balance their budgets, and by doing so year after year, and decades after decade, they have eventually built up unmanageable levels of debt. Taxpayers are used to spending money that they don't have, and they are generally not prepared to actually pay for the government services that they want.
We are now in a historical period when our mistakes are catching up with us. We got away with a lot of things for a long time. As a species, we have tended to act on the assumption that the resources of the world are infinite. This is proving not to be the case. The proverbial pigeons are coming home to roost.