If you're going to make an analogy, this is how you do it.
For the record, I don't always agree with Card. I happen to have little interest in his books, which leave me cold the umpteen times I tried to read them. "It's a Science Fiction Classic. . . "
On general principle, I despise analogies to the "Fall of the Roman Empire," especially those made by Fundamentalist Protestants who wish to attribute it to moral degeneracy. (For the record, the high point for moral degeneracy was the first century or two AD, before Christianity had any influence, and that was the most stable and peaceful era in history).
In general, folks who make big sweeping statements about the Fall of the Roman Empire know nothing more than that it "fell" a long time ago.
OSC is not that stupid. The statements he makes regarding the Western Roman Empire are correct--and the trade issue and collapse of civilized (meaning "centered on cities") life in the West are the major factors in the collapse, and the causes he discusses are broadly accurate.
I'm tracking the analogy to the modern situation. I don't know enough about economics in the 21st century (or, really, any century after the 17th) to be able to intelligently argue for or against his main argument. On the face of it, it sounds plausible to me