 Read the following passage:

"Ninian bought one of those smallish, almost identical houses that mushroom on the fringes of a city after every war, particularly where intensive bombing has created a number of desirable building sites."

What, in that passage, is symbolic?
No one, least of all Martin, could dispute that a man's life should be guarded by his kin—but by those who hadn't been born yet? Nobody in the neighborhood was surprised when Martin's mother disappeared and Ninian came to take care of him. He'd been a war baby, born of one of the tides of soldiers—enemies and allies, both—that had engulfed the country in successive waves and bought or taken the women. "He's dissatisfied with the current social order and killing you is part of an elaborate plan he's formulated to change it. But Ninian didn't know that and she went into a real tizzy, babbling that Martin had been sick and would make up the work. When it became clear that his mother was never going to show up again, Ninian bought one of those smallish, almost identical houses that mushroom on the fringes of a city after every war, particularly where intensive bombing has created a number of desirable building sites. There were hot water and heat all the time and a freezer well stocked with food—somewhat erratically chosen, for Ninian didn't know much about meals. The non-glass part of the house was of neat, natural-toned wood, with a neat green lawn in front and a neat parti-colored garden in back. Though they were in the house with him, in their minds and in their talk they were living in another world—a world of warmth and peace and plenty where nobody worked, except in the government service or the essential professions. There was no devastation, no war, no unhappiness, none of the concomitants of normal living. It was then that Martin began to realize that either the whole lot of them were insane, or what Ninian had told him at first was the truth. When Martin was sixteen, Raymond took him aside for the talk Ninian had promised five years before. We're virtually the same people ... although it is amazing what a difference two hundred odd years of progress and polish can make in a species, isn't it?" All that sort of thing comes from the out-system planets. And, on those worlds, it's far cheaper to use native labor than to ship out all that expensive machinery. In that way, there would be no space-drive, and, hence, the Terrestrials would never get to the other planets and oppress the local aborigines. Induced , Martin knew, could have meant anything from blackmail to the use of the iron maiden.
 "houses that mushroom on the fringes of a city after every war, particularly where intensive bombing has created a number of desirable building sites," is symbolic of the way things like the atom bomb, that leaves a mushroom cloud in its wake, are thought to have been unleashed upon the world to preserve or "create" things that will be "desirable" for society.
 "houses that mushroom on the fringes of a city after every war, particularly where intensive bombing has created a number of desirable building sites," is symbolic of the way things like the atom bomb, that leaves a mushroom cloud in its wake, are thought to have been unleashed upon the world to preserve or "create" things that will be "desirable" for society.  "intensive bombing" is symbolic of what the descendants imagine they are doing to Martin to make sure they impart enough of their future society on him to make him agreeable to carrying on with their way of life.  The word "bought" is symbolic of the wealth Martin is to bring to future worlds.  "Smallish, almost identical houses," is symbolic of the way that Ninian blends in with current society.