Federalist No. 5 again argues the value of union over confederacies of fully sovereign states. I see no reason to revisit the issue, but I did notice one very accurate prediction:
Whenever, and from whatever causes, it might happen, and happen it would, that any one of these nations or confederacies should rise on the scale of political importance much above the degree of her neighbors, that moment would those neighbors behold her with envy and with fear. Both those passions would lead them to countenance, if not to promote, whatever might promise to diminish her importance; and would also restrain them from measures calculated to advance or even to secure her prosperity. Much time would not be necessary to enable her to discern these unfriendly dispositions. She would soon begin, not only to lose confidence in her neighbors, but also to feel a disposition equally unfavorable to them.
As soon as I read this I saw its fulfillment in the conflict over slavery. One of the things that brought the Southern States to succeed was that President Lincoln was elected entirely on the strength of the Northern voters without ever appearing on the Southern ballots. The North had grown so much more important politically that the South felt compelled to separate themselves.