A Hymn Before Battle is the first book in John Ringo's Legacy of the Aldenata series. Earth is introduced to extraterrestrial life by the Galactics, who tell the leaders of the World that an invasion by another alien race, the Posleen, is coming. Earth's military forces are made available to the Galactics in exchange for technology to help stop the onslaught, but it is unclear just who can be trusted as the invasion nears. Source: Wikipedia (en)