If you observe the natural world, you will notice that animals migrate from one place to another in search of food. From the smallest to the biggest, they all do it in search of food. Since water is required to grow food, animals start to move season-by-season. Those movements give the television shows you can watch on Discovery channel and some other nature-related television channels and shows. And yet people don't accept the natural migration of the human animal. And today, we have debates about the immigration of human beings from one place to another on a worst yet imaginary line.
Humans migrate in search of better opportunities, which translates to job opportunities because the job market doesn't work in their place of origin or has been taken over by corrupt politicians. Still, in the end, those people move because they're looking for better employment opportunities that, in the future, will translate not only into food but other accommodations as well.
We, humans, have created systems of control. It doesn't matter what you call those systems, either Capitalism, communism, or any other ism. They are all systems of power, all a make-believe thing, and that is what the contract of society is; a system on which humans can coexist without having to kill each other for food and the resources needed to survive on this planet. But without those, we will not have a working society either, so we need them to have an organized human herd living together without being at each other's throats.
Many people migrate not only for resources but also because of circumstances outside their control, like wars and natural catastrophes. And yet war is another human-made situation.
Our systems are not perfect and require a lot of sacrifices, not to mention infinite growth. When it comes to humans, we can all be as corrupt as any other politician because power is what it does best; it buys souls.
As long as we have systems where someone else can buy, someone else will, and we will have those who will profit from war and the destruction of our planet and those who don't. Later, the same system will blame those trying to survive the consequences that those with power took and blame it on those with the least involvement. That is what immigration of the human herd is.
Those living in rich countries don't wish to see the less fortunate from developing nations migrate to their countries, but they do nothing to fix the problem. In contrast, rich nations create incentives for exploiting third nations' natural resources. Those same citizens do nothing when another war starts in another third-world nation or when corporations use political power to vent other countries to their will as the banana republics did in the past.
The migration of human beings will continue as long as resources are scarce in their local environment, as long as corruption keeps on buying wills, and as long as corrupt politicians and the rich decide to keep all for themselves and nothing for everyone else. And if you are an American living in America, eventually that same corruption will affect you too, to the point where you will have to flee your country too, just like many are doing it already.
Migration happens naturally in nature. And I will add that migration will occur on a system of controls humans create because we can all be corrupted, and we can't make perfect systems to control the resources our planet offers. When a system of control appears that may replace the old, you can bet those that benefit from the old will oppose the new.