Although the obvious reference is the children of Israel in Jerusalem, Jacob intends that his audience understand that this is one of the paths that they might travel. If they too become iniquitous, they too will read of the destructions, famines, pestilences, and bloodshed. All of those things have already been prophesied for the future Nephites if they are not righteous.
Both Nephi and Jacob understood scripture as a model for current behavior. Similarly, prophecy that affected one branch of the house of Israel could be applied to another. Although Jacob is describing a distant future in another hemisphere, he still intends that his audience apply that prophecy to themselves. They are to see themselves as possibly parallel to those in future Jerusalem.
Jacob has warned his audience that they are becoming iniquitous, and he is demonstrating how that iniquity works out in the future.