Periodically, one hears some, er, "reactionary" elements describe the movement of non-White persons into the United States or Europe as "colonization". "The Mexicans are colonizing Texas!" "The Arabs are colonizing France!" Given the history of how the United States got control of Texas, there is irony here. But it also got me to thinking -- when a person moves from the place they were born to another country, what distinguishes "immigration" from "colonization"? Both involve people permanently moving from political jurisdiction A to political jurisdiction B. But the former term is positive, happy, pursuit-of-happiness and land-of-opportunity. Even said reactionaries usually characterize their opposition as being to illegal immigration; as opposed to immigration generally which was the foundation of our nation. Colonization or colonialism, by contrast, is bad, evil, sounding in injustice if not outright theft of lands that rightfully belong to others.
So what is the difference? One answer is that we call the movement of people we approve of "immigration" and that which we disapprove of "colonialism". But that's not satisfactory -- it seems like there is an actual distinction here worth preserving. Another answer is that immigration is colonization where it does not come with the permission of the members of the destination polity. But if that's right, then the conservative immigration critics are right that illegal immigrants are engaging in acts of colonialism, which really doesn't sound correct to me.
Drilling further, it seems that a large part of colonization has to do with control. So maybe immigration becomes colonization if the new immigrant group wrests control over political outcomes from the prior residents. But once again, on reflection that can't be right -- it cannot be the immigration is permissible so long as the immigrants never end up winning elections.
Perhaps what's missing is the element of external control. When we talk about "colonialism", we usually have reference to a mother country. The United States was a British colony, Indonesia was a Dutch colony, the Congo was a Belgian colony, etc.. So maybe the mark of colonialism is that the new population wrests control over political outcomes and transfers it to a foreign entity. One colonizes on behalf of somewhere, one does not immigrate on behalf of anywhere. That seems to me to be the cleanest distinction, and the one that most closely coheres to the traditional model of colonialism (colonies and parent nations). But maybe it also suffers from inadequacies -- I'm happy to hear suggestions. But the point is it seems like we don't have a strong distinction of when people have a right to move to a new location (indeed, it's praiseworthy or at least respectable) versus when it is improper. This leads to considerable conceptual fuzziness; it also buttresses anti-immigrant sentiment insofar as it poses too-strong rights claims on behalf of those who happen to be residing on a plot of land at some arbitrary prior point in time.