Natural disasters, whether caused by floods, forest fires, tornadoes, volcanic eruptions, earthquakes or tsunamis, are calamitous events for a human community. Recall, in our lifetime, the Indian Ocean Tsunami in 2004 that killed 230,000 people in 14 countries, and the earthquake last week in Nepal that resulted in the death of well over 5,000 souls. There’s nothing we can do about these events — man is helpless in the face of nature’s wrath — other than rebuild and move on.

But what do we do in the face of disasters induced by the human condition, by social, political and economic forces of one’s own making? Take the phenomenon of emigration from what demographers and economists call countries in the South to those in the North, or what we mortals call the transfer of populations from the impoverished lands to the more prosperous ones in Western Europe and North America.

In recent years, thousands have died on perilous journeys of hope in search of that City Upon the Hill — 800 in the Mediterranean last week alone — only to find hostility awaiting them in their host states. How do we explain this phenomenon? Why do emigrants risk their lives, leaving home and homeland behind, to brave dangerous seas and deserts in order to reach a land they suspect replete with milk and honey only to find it leveling rejection and scorn at them?

To be sure, migration is as old as history. Since around 3,000 BC, various clearly identifiable peoples, including individuals, family units, large communities, even whole tribes, have moved from one area to another and mingled peacefully with the native peoples they encountered there, in the bargain profoundly influencing the human story. Conversely, where they arrived with hostile intent, as say did the Huns and the Vandals in ancient times, or Dutch Afrikaners and European Jews in modern times, war and mayhem would follow their advent. But one thing is plain: There has always been population transfers. Those who assimilated prospered, and those who sought conquest perished.

Since the beginning of the second half of the 20th century, migrants have been on the move again. Certainly over the two decades or so, as any newspaper reader will tell you, these lost souls — what Franz Fanon called “the wretched of the earth,” coincidentally the title of his 1961 iconic book — have risked their lives, say to trek across the forbidding terrain between the US and Mexico to reach “the land of opportunity,” or to sail on rickety boats across the choppy seas of the Mediterranean to reach countries in the European Union.

And try as hard as they could, neither authorities in the US — which has spent a staggering $15 billion on immigration enforcement — nor those in the Europe have been able to plug the flow. So again: Why do migrants, at such great risk, continue to seek refuge in these countries? The answer is as banal as it is poignant —desperation. You are desperate when you flee lands, where political instability undermines livelihoods and war threatens lives. And you are desperate when abject poverty and political repression can reduce your humanity to a fragment. Migrants know they are not wanted in the countries they seek a haven in, yet they keep coming, driven by human needs almost outside their control. Let’s face one fact: The anti-immigrant sentiment is now out in the open. A majority of Europeans would like to see fewer immigrants, or ideally no immigrants at all, allowed into their countries. Immigrants, the visceral argument goes, cannot, or do not want to, assimilate. They take jobs away from the locals. They are lazy. They are freeloaders. They consume social benefits that belong to citizens. And the rest of it.

Let’s face another fact: This nativist sentiment also met immigrants who began to arrive in the US around the middle and late 19th century, and who, like their counterparts in rickety boats in the Mediterranean, sought to escape war, poverty and repression. After those Irish migrants who fled the potato famine in their land in the 1840s, for example, arriving in the US — hungry, destitute, with lice in their hair, having traveled across the Atlantic in steerage — to meet with “the Irish need not apply” signs. Yet these folks went on to fight in the Union Army. They made up the majority of the labor force that built America’s railroads “from sea to shining sea.” And, lest we forget, one of their own became the 35th president of the United States.

Other immigrants were to fare no better, for they kept coming, undeterred by the discrimination they knew awaited them. Overpopulation in Europe at the time, coupled with the promise of opportunity and riches in America, led more than 30 million of them to seek new lives in the New World. And let’s not forget the Know Nothing Party in the 1850s, the national movement that promised to “purify” American politics by limiting, or ending altogether, the influence of Catholics, whether they were Irish, Italian, German, Polish or whoever — America was to remain a Wasp nation, White, Anglo, Saxon and Protestant. Shades of Europe’s insecurity today about its entrenched notions of identity? Looks like it.

Whether we’re talking about immigration in Europe or the US, immigrants are on the move, just as their ancestors in antiquity had been in the Fertile Crescent, where immigration first became fashionable, where the first human civilization had flourished and where three great religions were born. Europe is what Europe becomes. And America can no more live without immigrants than fish can without water. By 2030, after more than 30 million baby boomers would have retired, the nation will wish to have more, not less, immigrants. So will Europe. And trust me on this one: Their wish will be granted.