The United States' student debt crisis has become a hot-button issue in this presidential campaign But how, exactly, did we get here in the first place? Well, we're here to break it down.In 1993, college students graduated with an average of $10,000 each in loan debt. By 2015, they had an average of $35,000 . Almost 70% of students who earn Bachelor's degrees have at least some student loan debt. That means there are 40 million people in the United States who collectively owe $1.2 trillion in student loan debt.As this video explains, part of the blame lies with the American economy itself. Workers haven't been receiving raises, which means there's less money to save for college tuition, leading to more loans. On top of that, tuition costs have risen, partly because there's been less state and federal funding for state schools since 2008. And the icing on the cake? American workers often don't make enough money to repay their student loan debt, even if they're employed in fields that require college degrees. Of those who began paying their loans back in 2011, nearly 14 percent had defaulted within two years. It's no wonder that our recent Vote Your Values poll , conducted in collaboration with ABC News, found that 21% of millennial women view student loan debt as the most important issue to them this election season. To find out where the leading presidential candidates stand on student loan debt, click here