Nightwings by Robert Silverberg
Robert Silverberg (born 1935) is a remarkably prolific science fiction writer who is always competent but also capable of genuine beauty. This novel from 1969 portrays an Earth of the very distant future in which human society has become frozen into a rigid inflexible guild system devoted to being on watch for an alien invasion. While Silverberg's ironic edge is never far away, the book presents a fascinating future history and has moments of beautiful lyricism and humanity.
I should add one more thing about this fine writer. Here is an assessment of him from the
Science Fiction Encyclopedia
" For more than half a century, his productivity has seemed almost superhuman, and his abrupt metamorphosis from a writer of standardized pulp fiction into a prose artist was an accomplishment unparalleled within the field. He was elected to the Science Fiction Hall of Fame in 1999, and in 2004 received the SFWA Grand Master Award. In the early twenty-first century, he remains one of the most imaginative and versatile writers ever to have been involved with Genre SF, which he was instrumental in transforming after about 1970. His relegation to the sidelines by the American literary establishment is scandalous". [BS/JC] - See more at:
http://www.sf-encyclopedia.com/entry....H2Ao1GXB.dpuf