A significant part of the population of the United States is alarmed about what it thinks is an enemy army approaching our southern border — a collection of rapists, MS-13 gang members, middle eastern terrorists and zombies intent on forcing their way into the country in order to destroy our society and culture. One of our citizens became so anxious about this invasion, which, he had it on good authority, was being financed by Jews, that on Saturday he went into a synagogue in Pittsburgh and killed 11 people.

The information about the content and intentions of this caravan, as it is being called, first came to public attention almost exclusively through fulminations on Fox News and subsequent tweets from the Tweeter in Chief of the United States. (Except the part about the zombies, I made that up. But there are still a few days until the midterm elections. Watch that space.) The entire FoxTrump Tango has been a pathetically transparent attempt to scare the bejesus out of American voters so they will gallop out and vote for the wall, or whatever.

But the debunkers of this fairy tale have not done their job. Yes, they have shown us — those of us who will look at contrary evidence, such as, you know, photographs — that this is no army, but a ragtag procession of families, many women and small children among them, stumbling 30 miles a day through blistering tropical heat in the hope of asylum in the United States — protection for which they are entitled to apply under the laws of this country.

But the bunkers and debunkers of this story all seem equally oblivious to the root cause of the migration, the reason so many parents have undertaken this arduous, thousand-mile trek toward uncertainty. Spoiler alert: It’s not, as the perpetrators of this fantasy would have you believe, because they are lazy and want to get on welfare; or because they are criminals in search of new victims; or terrorists who hate us because we’re free. Nor is it sufficient to assume, as the mainstream media do, that they are intent on moving away from crime-and-poverty, like so many yuppies who have read the Chamber of Commerce brochures and are making a career move.

I hold the view — a minority opinion, apparently — that understanding why people act as they do is a prerequisite for influencing what people do. But comprehending motivation requires empathy and intelligence, both of which seem to be in scant supply in our political life. A corollary notion is that understanding the forces acting on these people might prepare us for dealing with those forces when they get around to acting on us.

Here’s what no one wants to tell you, or hear: the thousands of people who have left their homes in Guatemala, Honduras and El Salvador to risk their lives and their childrens’ lives in search of a better life are fleeing the longest and most vicious drought in the history of the region. They are climate refugees, and they are only the vanguard.

For at least five years, drought in Central America’s Dry Corridor has been intensifying, causing ever worsening crop failures, food shortages, water insecurity, unemployment and migration. Guatemala ranks as one of the ten countries in the world most vulnerable to climate change. Last year the UN’s World Food Programme asked a sampling of migrants why they had left their homes in the Dry Corridor. By overwhelming majorities, they cited not crime-and-violence, but the drought and its many offspring. Nearly half cited hunger.

Our society and culture will be destroyed not by desperate families seeking a better life, but by our ignorance and greed and refusal to understand what is happening here, not just to unfortunate brown people from other countries, but to all of us on this planet. There will be many more caravans, larger ones, from Central America, and then they will be trudging out of our own America — from uninhabitable zones in Arizona, Nevada, central California, and from the inundated coasts of Florida and the Carolinas.

The caravans are coming, and hell’s to pay.

[UPDATE: The Guardian of England, frequently the best source of American news, agrees: “The unseen driver behind the migrant caravan: climate change”]