I read sometime ago a short sci-fi story.
It's about 2 astronauts from Earth traveling to an other planet. On their way to that planet they get intercepted by an alien vessel. The captain of that ship tells the 2 astronauts about an enemy that kills billions of aliens in the milky way. There was a big war and the bad aliens got killed, but they send ships out to search if there were more. When one of the astronauts asks if they ever found one of the enemies, the captain said not till today.