"Collision Course" is a 1961 science-fiction novel by Robert Silverberg, published as one-half of an Ace Double, along with The Nemesis from Terra, by Leigh Brackett. At 130 pages, "Collision Course" is a longer story than most for the Ace format, which is good, because a lot happens here.
It is about seven hundred years in the future, and humanity has expanded to colonize planets around other stars. Up until now, this has been done with slower than light starships, paired with instantaneous "transmat" (basically like a Star Trek teleporter) between established planet. However, as the book's opening chapter describes, humanity has just discovered its first warp drive, explored beyond their borders, and also discovered their first alien race. When Technarch McKenzie learns about this, he gathers together the "Archonate", a governing body of technocrats, and gathers together a team of negotiators to go divide up the galaxy for colonial expansion. The leader of the negotiators, Dr. Martin Bernard, is a sociologist, and is the book's main protagonist. The other members are a diplomat, a biophysicist, and a linguist, Havig, whose "neopuritan" religious faith causes friction with the other members of the team.
One thing that I liked in this introduction is how economically Silverberg establishes a complex society. The "Archonate" is hierarchical and limits expression, but it is not portrayed as dictatorial or dystopian. The book criticizes the idea of a technocracy, but it does it slowly.
The party meets the aliens, and after establishing the process of getting culturally acquainted (something that at another time might have fell under the editor's pen in an Ace Double), the book reaches its first conclusion: the aliens, called the Norglans, while neither militaristic or bloodthirsty, tell the human delegation that they must stay within their established stellar systems, and that the rest of the galaxy is for the Norglans. After digesting this news and feeling some angst about the possibility of either humanity being trapped, or of an intergalactic war, the ship's warp drive goes astray, and they are transported to the Magellanic Clouds, where in a sudden twist to the story, super-super advanced aliens turned out to be watching them all along, who then retrieve the Norglans instantaneously from across the galaxy, and force a peace treaty on all of them. (This seemed someone reminiscent of the Star Trek episode "Errand of Mercy", with the Organians forcing peace on the Federation and Klingons, although this was written at least six years before). The book ends with peace reestablished, and with the realization that man's place in the cosmos has changed. (And yes, here, it is "man's place in the cosmos", which I will discuss below.)
What I liked about this book is how it managed to balance so many things in so short a time. The book starts out as rather hard science-fiction, with the technology and sociology of the society described in a consistent manner (unlike, for example, "The Light of Lilith", published around the same time, whose science and technology was a type of dream logic), and the book also covers the "action" parts of a science-fiction story in detail, using the journey through space and planetary exploration as a way to introduce interesting details and also add to character development. The "first contact" is also done well, and we are presented with aliens who aren't bug eyed monsters but are still adversarial. Then, the book introduces something else: the idea of massively powerful aliens beyond human understanding, ending with a philosophical take on hubris and potential. It is a lot for a 130 page book!
One thing that I have said before about Ace Doubles, and by extension, about post-war Science-Fiction, is that it is less militaristic and chauvinistic than it is remembered. At the start of this book, it seems the author is promoting the idea of technocracy and militaristic colonialism, but by the end of the book, that is clear it is not the case. But this book does have a huge, glaring flaw that would be part of the case against the era's writing: there are no female characters in the book. A few women are mentioned in passing as background characters, but every character who speaks or does anything in this book is a man, and it is, as I said, about man's place in the cosmos. (The book does actually point out in an aside that humanity has moved past racism, but apparently not sexism). This makes the book both less interesting in its sociological message, and also less fun to read, as all-male character interaction can be a bit boring. So despite much of the criticism leveled at pulp-era science-fiction being unfair, charges that it lacked gender diversity were often very true.