The answer, according to researchers at Queensland University of Technology in Australia, is fear and anger.
The first-of-its-kind study analyzed the personality traits of millions of US and UK voters through an online test. Although personality traits haven’t really influenced voters before, it seems these elections were different.
Both campaigns were heavily fear-based, populist movements. This means that people who have traditionally neurotic personalities are more likely to vote for the option that offers a means to lessen that fear.
The researchers found that in places that have a lot of psychological hardship, voters were particularly likely to respond to political campaigns based on fear.
They also found that this sort of voting is shaping the global political landscape, since populism is becoming a lot more popular among campaigns, and this plays to people's fears.
Also, the results of the two elections were largely dictated by voters that were suffering from both emotional and economic problems.
Long story short: fear works, and we’re likely to be seeing more of it.