Why? Because there were two superpowers competing for your affection by throwing foreign aid at you, building your army, buying your cheap goods and educating your college students ; climate change was moderate; populations were still under control in the developing world; no one had a cellphone to easily organize movements against your government; and China was not in the World Trade Organization, so everyone could be in textiles and other low-wage industries.

All of that switched in the early 21st century: Climate-driven extreme weather — floods, droughts, heat and cold — on top of man-made deforestation began to hammer many countries, especially their small-scale farmers. This happened right as developing-world populations exploded. Africa went from 140 million in 1900 to one billion in 2010 to a projected 2.5 billion by 2050.

Syria grew from three million people in 1950 to over 22 million today, which, along with droughts, totally stressed its water resources. Guatemala, the main source of the migrant caravan heading our way, has been ravaged by deforestation thanks to illegal logging, farmers cutting trees for firewood and drug traffickers creating landing strips and smuggling trails.

A satellite map just released by University of Cincinnati geography researchers demonstrated that nearly a quarter of the earth’s habitable surface changed between just 1992 and 2015, primarily from forests to agriculture, from grasslands to deserts and from wetlands to urban concrete.

Meanwhile, the internet has enabled citizens to easily compare their living standards with those in Paris or Phoenix — and find a human trafficker to take them there. Also, China joined the W.T.O., dominating low-wage industries, and the end of the Cold War meant no superpower wanted to touch your country, because all it would win was a bill.

So it’s now much harder to be an average little country. The most frail of them are hemorrhaging people, like Guatemala, Honduras, El Salvador, Sudan and most every nation in sub-Saharan Africa. Others — Venezuela, Syria, Afghanistan and Libya — have just fractured .

Together, they’re creating vast zones of disorder, and many people want to get out of them into any zone of order, particularly America or Europe, triggering nationalist-populist backlashes.