I am left with the impression that "ethno-nationalism" is a word that has been invented by a marxist. It portrays dirtily what is none other than simple patriotism, that is to say, love of one's fatherland.
Fatherland, that is, nation, which comes from the latin word natus, meaning born, intrinsically implies the idea of a "people," a very large family, if you will.
Love towards Fatherland is a good thing. In fact, St. Thomas says that Piety, which moves man to love God, moves him also to love his parents as well as his country (IIa IIae, Q. CI, AI).
It follows that a man should prefer the members of his family to complete strangers, his fellow citizens to aliens.
To apply this idea concretely,(I apologize in advance to any politically-correct Catholics on this thread) an American should not feel any obligation to invite aliens unconditionally into his country in order that they enjoy the fruits of the USA. We citizens could eventually have an obligation in charity to help our neighbours in times of true distress. We are not, however, obliged in Justice to allow Mexicans into our country only that they may enjoy a better life.
"But the suffering!....."
No.
Mexicans may live in worse conditions than Americans, but they do not live in misery. The fact that some people be poor is not a crime crying out for vengeance.