How does the author use foreshadowing in The Conquerors?

McGinley notes that with the mechanized catapult, the first having been built around the middle of the third century B.C., a large stone or javelin could be hurled anywhere from four hundred to eight hundred yards. Not only did this add power to the weaponry, it also allowed the two warring parties to fight at a distance from one another. This was a precursor of the atom bomb, which could be dropped from an airplane at a distance of thousands of feet. One result of this invention was that the aggressor could kill his so-called enemy without ever humanizing his target. With McGinley's mention of the catapult, readers gain the sense that she is giving them a progressive report of the development of weaponry, which foreshadows the Americans' atomic bomb.