It just breaks my heart to actually see a country the world looked up to, a place where I have family that are the kindest people turn into this.

Basically, people's lives steadily got worse. Real income fell for the majority, many lost their homes during the crash, jobs are harder to come by (collapse of the middle class in the US, bad recovery from the crash in Europe) and in general people are feeling scared and helpless.

You didn't consciously notice this gradual creep because it occurred over the span of twenty or so years. And people had no way to express their worries - if you dared speak up, you were lazy/a racist/intolerant/a luddite/etc.

While the old world order looked great on the surface, people were growing more and more unhappy. Clinton's outright disdain for people's concerns caused tensions to boil over in the US. Trump didn't just promise to make things better for the common man, but also to slam the uncommon man's face into the pavement, offering sweet revenge. Meanwhile the European dream fell to pieces during the crisis when countries were at each other's throat and politicians refused to lower taxes, reduce government debt or do anything at all to create more jobs for the people they were supposed to represent.

So no, people didn't "suddenly" turn into assholes. They just finally saw an opportunity to vent all of their stored anger, frustration and despair at once.