Tens of thousands of Central Americans, many of them unaccompanied children and teenagers, have flooded into the US illegally in recent years: they are a growing part of a human tsunami that has hit the southern border and caused what many refer to as a humanitarian crisis, overwhelming the local and federal authorities – and becoming a major political issue.

On the one hand, we have immigration restrictionists like Donald Trump, who say that "we cannot be a country and have no borders," and who vow to build a Wall – "and make Mexico pay for it." On the other hand, we have Hillary Clinton, who says we should be "knocking down barriers, not building walls," and claims that Trump and his supporters are motivated by "bigotry."

Like most partisan political debates, this one gives off plenty of heat without shedding much light. Because the real question is: why are hundreds of thousands of people suddenly abandoning their homes, their families, and their countries to make the long and dangerous trek through Mexico and into the United States? And where are these people coming from?