The Xenogenesis series starts with the book Dawn, and includes the novels Adulthood Rites and Imago. In Dawn, Lilith Ayapo had just lost her husband and daughter when the earth is destroyed in a nuclear war. She wakes up two hundred years later on an alien ship that is orbiting the now lifeless planet Earth. Just as the bombs were dropping, the aliens transported thousands of humans to their ship to save humanity from extinction, and to repopulate the Earth once it is safe to do so. But the aliens aren't just doing it out of the kindness of their hearts (or whatever organ stands for goodness in their culture). The race of aliens that has saved the humans survives by traveling the stars, interacting with other species, and taking some of their genetic traits into themselves. Basically, they mean to procreate with humans to capture their genetic material, and the reward is the continuation of the human species. As you can imagine, this does not sit well with many of the humans, who see the aliens as their jailers, not their saviors.
Superior alien technology means that while the aliens try to get consent, they can basically take what they want, so humanity's resistance is pretty futile. Adulthood Rites and Imago take the story from the ship down to Earth, and through at least two generations of both humans and aliens. The story explores the idea that humanity has two fatal flaws that will always cause violence and destruction; intelligence and a desire for hierarchy. Because humans believe in hierarchy, they will always try to assert dominance. Because they are intelligent, their attempts to dominate each other can be incredibly destructive. The novels also explore the idea that humans feel threatened by anyone who does not resemble themselves, which in this case leads to some memorable conflicts with the aliens, but is also a symbol for the way humans have used everything from the shape of someone's eyes to skin color as an excuse to "other" people who are different than them. This "othering" allows humans to justify their domination, repression, and genocide against each other.
Unlike some of Butler's books, the message behind this story is pretty clearly stated by the aliens as they strive to teach the humans how to overcome their violent natures. There are plenty of examples of this human flaw, from when Lilith fights against her alien captors on the ship to the so-called resistors on Earth who try to escape the influence of the aliens. The human tendency for violence is starkly contrasted against the alien culture, who do everything in their power to avoid violence, and who are constantly at a loss for why humans would do so much that undermined their own existence.
The aliens are not perfect, though. While they are a less-violent people, they do have their own caste system. There are three basic types of aliens, and each has its own specific role in their society. To some extent, these roles are in fact defined by their biology-the three types of alien are different in form and function. But any deviation from those roles is met with disapproval and sadness on the part of the others, and extreme cases of dissatisfaction with one's purpose in life are dealt with through exile back on the ship.
Butler's creation of the alien race is unlike anything I'd read before. So often, aliens in science fiction are portrayed as inhuman monsters, or they are created in a human's image. These aliens felt just that-alien. Their cool assessment of human nature is something that is hard to deny, given our millennia of history and their almost incessant wars. Once again, Butler has shown us something about ourselves that is discomforting at best, and monstrous at worst, but that we must confront if we ever hope to move past the divisiveness of racism, classism, sexism, etc...that has defined our societies thus far.
