Cool presentation simultaneously of a post-apocalyptic setting and a geocentric aliens narrative. The aliens aren't quite right, but they're not caricatures of the genocidal maniacs from Wells, either--they conceive of themselves as "traders," mostly in genetic material, and they appear to be pure democratic-commies, too, making decisions by consensus.
The "trading" stuff means mating between human persons and alien persons, which could be a kinda gross exercise in tentacle porn, but just ends up being some weird neurological manipulation along with genetic engineering & in vitro fertilization. It's all complicated by the fact that the aliens have three sexes, and much of the narrative involves exploring the third sex, which is not a neuter, but has an active role in reproduction. The complication results in hybrid children having two human parents and three alien parents.
Novels also very reasonably have a limited northern hempsiphere cast because the US & USSR destroyed the northerners in nuclear war. A bit gender essentialist with regard to humans and aliens at times. Also, annoyingly represents humans as suffering from a fundamental genetic contradiction between intelligence and hierarchical behavior: humans naturally destroy themselves. Not my belief, but there it is.
Much of the narrative involves the problem of post-apocalyptic human fertility--we've been rendered sterile and can only reproduce in conjunction with aliens (lotsa G-rated tentacle porn, really). Some folks dig that, but others resist it. In the context of this conflict, then, one of the hybrid alien persons essentially becomes the attorney for the humans who resist commingling with aliens.
Recommended for all speculative fiction readers.