The central fact of migration is that it is heavily path dependent, an idea laid out many years ago in Paul Collier’s Exodus. The number of people willing to move, in a world where travel is relatively cheap and safe, where wages are far higher elsewhere and established communities have already settled, is vast. This has already been illustrated by the natural experiment of North Cyprus, an unrecognised state in which citizens have the right to move to a richer country (Britain), and in which citizens of a poorer country (Turkey) have the right to move to. As a result, more Turkish Cypriots now live in Britain than in Cyprus, where they are outnumbered by Anatolian Turks.
– Ed West

In which Ed West proves that stuff flows uphill. 😉
The present mass migrations (and the natural increase, births, of hostile populations) is nothing to do with libertarian free migration – as it is fueled (contrary to dishonest denials – including by some libertarians), by government benefits, public services, and “anti discrimination” regulations and policies – none of which would exist in a libertarian society.
In some countries, such as Germany, the hostile migrants were actively invited in by the government – in either an act of insanity, or out of hatred, hated by the establishment, of the historic population of the nation.
In American cities, such as New York, the migrants are given, at taxpayer expense, accommodation (sometimes in expensive hotels), benefits, medical care, and-so-on. And in Britain not only are benefits and services thrown at the invaders (as the migrants are clearly hostile – the word “invaders” is not unfair) – but calls to resist them are sometimes punished with imprisonment.
Again – it should be obvious that none of this is really libertarian free migration, and it is clear that the goal of the Western establishment is NOT the assimilation of the migrants or their children or children’s children – for example the Western establishment makes no effort to convert people from Islam (a world-view that has been in conflict with the West for many centuries – and whose doctrines are not compatible with the West) – on-the-contrary, the Western establishment constantly praises Islam – and persecutes people who oppose it.
By a combination of “Progressive” “Social Revolution” policies (since the 1960s) aimed at reducing the fertility rate of historic nations, and by encouraging the immigration and natural increase of hostile populations, the establishment is destroying the Western world – whether the destruction of the West is the deliberate aim of the establishment, or whether this is all just folly (folly on an incredibly vast scale), I leave for others to judge.