Rings of Saturn’s seemingly random topic hoping is all coming together, related in the big picture by every thought, every piece of history he talks about seeming to show how humans are terrible, or maybe that the world is terrible.
Aside from the overt bleakness of the historical stuff he talks about, there is a subtle kind of darkness overlaying everything, just in the way he describes things. Below is a section for example, when he sees some people below him at a beach:
I crouched down and, overcome by a sudden panic, looked over the edge. A couple lay down there, in the bottom of the pit, as I thought: a man stretched full length over another body of which nothing was visible but the legs, spread and angled. In the startled moment when that image went through me, which lasted an eternity, it seemed as if the man’s feet twitched like those of one just hanged. Now, though, he lay still, and the woman too was still and motionless. Misshapen, like some great mollusc washed ashore, they lay there, to all appearances a single being, a many-limbed, two-headed monster that had drifted in from far out at sea, the last of a prodigious species, its life ebbing from it with each breath expired through its nostrils.
There are many ways one could describe a couple having sex on the beach… this way of doing it is certain to create a strange, creepy feeling for the reader…