The circumstances that brought the boys to the island were war and the lack of adults.
During World War II, it was fairly common practice to ship children out of London to keep them safe. This is the backdrop of Lord of the Flies, which was written after World War II and partly in response to the dark side of human nature seen then.
A group of British boys were traveling by plane to Australia, but the plane crashed and they were stuck abandoned on an island. The plane was attacked, fell into two parts, and crashed. None of the adults actually survivd.
“Where’s the man with the trumpet?”
Ralph, sensing his sun-blindness, answered him.
“There’s no man with a trumpet. Only me.” (ch 1)
Specifically, the boys are stranded on a deserted tropical island without adults. It is the circumstance of having no adults that really creates the setting for the story. Everything would have been different if there had not been at least one adult, and the boys had not been left to their own devices.
Despite the timing, the book is not actually set during World War II. There is no specific war mentioned, and no specific enemy. Clearly, Golding is depicting the world at war and the war within the human heart as a constant.
Lord of the flies is a malicious vision of human nature and a reflection of the lurking evil, that lies beneath the aphotic side of the human psyche. It was inspired by the horrors of Holocaust and the second world war. The events described in the novel are reminiscence of the vilest manifestations of Nazi regression. The novel opens with a group of 25 pre-adolescent British boys, marooned on a desolate coral island in the Pacific ocean, completely free of adult supervision or intrusion. Actually, these boys survive an aircrash, while being evacuated from England, on account of an imminent nuclear war. They were being taken to Australia, when the aircraft was struck by a bomb, killing all the adult members on board. The boys, however, escaped through the passenger tube of the aircraft.