A nation is a people not a border. There is no Catholic reason for it that I can see, but I haven't read the brief. I'm sure they make an argument from charity, but charity for whom? Given the USCCB's questionable involvement with certain funding channels, I would prefer they stay out of it and tend to the salvation of souls. We need good bishops who are not beholden to the civil authority. Hard to do when the faithful are economic slaves but that just makes it more important to do.