Decision at Doona was published in 1969 byAnne McCaffrey, In this book, two races, both living on overcrowded world, decide to live on the same pastoral planet at the same time. Once they discover each other, both are wary, but quickly learn to overcome their differences. However, each believes that only misery will come from cohabiting with another race, and their laws forbid it. If not for the out-of-control and headache inducing son of the main character, all might be thrown to ruin.
Due warnings: The science, tech, and social relationships are archaic. The inherent sexism of the age shows. There are more than a few things contrived. It's all part of the age. At least nobody smokes. There's even the period lack of characterization.
The book reads like an SF version of Dennis the Menace collided with Gunsmoke, with some Lassie thrown in as well. The motivators behind the book are not violent, but social. So lost kids get lost, herds stampede, and barns get raised. And worse of all, the government gets involved, and that's where the major trainwrecks threaten. Fortunately, the book never devolves into Libertarian World.
The story sometimes flounders a bit, making choices that we would consider odd, but fit perfectly well within its own time. The idea is there more than the story. Despite that, I have a great respect for the book, for writing an SF novel without violence as the narrative backbone is harder than it looks.
This may not look like a watershed book to you, but it is for Anne. This book contains the blueprints for all the future dragon rider books. The colonists here have purposely chosen a lower-tech lifestyle, an idea that returns in future McCaffrey books. This novel centers around social conflict, differing goals, rather than the fight. Strangely, there aren't any psychics at all, which is pretty rare for an early McCaffrey.
I suppose that the novel examines race-relations of the age, an allegory of black and white living together. The late 60's were a terrible time in race relations. The book shows that despite laws, both races have the same goals of living good lives, and it's up to the ordinary person to seize that. Mutual cooperation will breed mutual respect and bring blessings to all.