In G. K. Chesterton's day, Catholics in England were suspected of being beholden to foreign influence and inadequately patriotic. Chesterton was himself quite patriotic, which he defended as a natural virtue which was -- he insisted -- not a denial of universal Christian brotherhood -- but rather its natural analogue.
[The Christian] religious culture does indeed encourage [the Christian] to fight to the last for his country, as for his family. But that is because the religious culture is generous and imaginative and humane and knows that men must have intimate and individual ties. But those secondary loyalties are secondary in time and logic to the law of universal morality which justifies them.
Note: Chesterton appeals -- not to universal fellow-feeling (which simply does not exist, any more than a mother or father can credibly claim to love other children as passionately as their own). Rather Chesterton appeals to universal morality, which -- until postmodern relativism came along -- did exist and continues to exist in reality, if not in the sentimentalized imaginations of contemporary "citizens of the world."
As for the virtue of patriotism, Chesterton writes "I have always done my best to defend it, though I have sometimes become suspect by sympathizing with other people's patriotism besides my own."
But I cannot see how it can be defended except as part of a larger morality; and the Catholic morality happens to be one of the very few large moralities now ready to defend it.
Again, what Chesterton calls the "human unity anterior to all these healthy and natural divisions" is rooted in a moral truth, not in some seamlessly uniform affection for "humanity." Eliminate that moral truth by, for instance, refusing to acknowledge the existence of human nature deserving of inalienable dignity, and all the solemn and pious invocations of devotion to "humanity" or, God save us, "the planet," etc. will lead further and further into an abyss of lovelessness masquerading as lofty principle.
Capturing the essence of what Philip Rieff calls the transgressive nature of contemporary cultural life and its deleterious effects on comity and a sense of shared principles, Chesterton offers this:
Religion is of the heart, not of the head; and as long as all our hearts are full of hatred for everything that our fathers loved, we can go on flatly contradicting each other for ever about what there is to be hated.