"The Catholic Church is by far the largest, the most widespread, and the most ancient of Christian communions in the world, and is moreover the mighty trunk from which the other communions claiming to be Christian have broken off at one time or another. If, then, we limit the application of the term Christendom to this, its most authentic expression, the unity of Christendom is not a lost ideal to be recovered, but a stupendous reality which has always been in stable possession. For not only has this Catholic Church ever taught that unity is an essential note of the true Church of Christ, but throughout her long history she has been, to the amazement of the world, distinguished by the most conspicuous unity of faith and government, and this notwithstanding that she has at all times embraced within her fold nationalities of the most different temperaments, and has had to contend with incessant oscillations of mental speculation and political power. Still, in another and broader sense of the term, which is also the more usual and is followed in the present article, Christendom includes not merely the Catholic Church, but, together with it, the many other religious communions which have either directly or indirectly, separated from it, and yet, although in conflict both with it and among themselves as to various points of doctrine and practice agree with it in this: that they look up to our Lord Jesus Christ as the Founder of their Faith, and claim to make His teaching the rule of their lives. As these separated communities when massed together, indeed in some cases even of themselves, count a vast number of souls, among whom many are conspicuous for their religious earnestness, this extension of the term Christendom to include them all has its solid justification. On the other hand, if it is accepted, it becomes no longer possible to speak of the unity of Christendom but rather of a Christendom torn by divisions and offering the saddest spectacle to the eyes. And then the question arises: Is this scandal always to continue? The Holy See has never tired of appealing in season and out of season for its removal but without meeting with much response from a world which had learnt to live contentedly within its sectarian enclosures. Happily a new spirit has lately come over these dissentient Christians, numbers of whom are becoming keenly sensitive to the paralyzing effects of division and an active reunion movement has arisen which, If far from being as widespread and solid as one could wish, is at least cherished on all sides by devout minds." https://www.newadvent.org/cathen/15132a.htm

Christopher Columbus, who I believe was saintly and should be canonized as a Saint, first discovered America and consecrated it to Our Lady. I believe he sailed in a vessel that was named after Her Immaculate Conception.

Anyway, here is Pope Leo: "We traverse in spirit and thought the wide expanse of ocean; and although We have at other times addressed you in writing - chiefly when We directed Encyclical Letters to the bishops of the Catholic world-yet have We now resolved to speak to you separately, trusting that We shall be, God willing, of some assistance to the Catholic cause amongst you. To this We apply Ourselves with the utmost zeal and care; because We highly esteem and love exceedingly the young and vigorous American nation, in which We plainly discern latent forces for the advancement alike of civilization and of Christianity.


https://www.vatican.va/content/leo-xiii/en/encyclicals/docuмents/hf_l-xiii_enc_06011895_longinqua.html

Finally, even if a nation was never Catholic, every effort must be expended toward making it Catholic Christian anyway. But America does in fact have Catholic roots, together of course with some Protestantism, a little Deism etc.

Your propaganda is getting old!  The United States has NEVER been a Christian nation.  From its foundation, the US has been Masonic (naturalism, rejecting grace) and inhabited by heretics.  Heretics hold some Catholic truths but reject others. They reject the means of grace and therefore live in mortal sin, cut off from Christ.  They are not Christian but rather, follow false christs of their own imagining.  Making God in their own image and likeness.
God created all souls with natural virtues but that will not save them, neither does it please God.