It may perhaps be thought superfluous to offer arguments to prove the utility of the union, a point, no doubt, deeply engraved on the hearts of the great body of the people in every State, and one, which it may be imagined, has no adversaries. But the fact is, that we already hear it whispered in the private circles of those who oppose the new Constitution, that the thirteen States are of too great extent for any general system, and that we must of necessity resort to separate confederacies of distinct portions of the whole. This doctrine will, in all probability, be gradually propagated, till it has votaries enough to countenance an open avowal of it. For nothing can be more evident, to those who are able to take an enlarged view of the subject, than the alternative of an adoption of the new Constitution or a dismemberment of the Union. It will therefore be of use to begin by examining the advantages of that Union, the certain evils, and the probable dangers, to which every State will be exposed from its dissolution. This shall accordingly constitute the subject of my next address.
This is from the Federalist Papers. But I don't understand the first sentence. The noun alternative is used here like the choice between A and B... Why?