I read this book about 6-Feb-2008. I've read this book before. The book is copyright 1961. This note was last modified Wednesday, 20-Feb-2008 07:54:53 PST.
This note contains spoilers for the book.
An obscure Doc Smith book from 1961/62 (serialized in If). Project Gutenberg has just released it, which is nice. E. Everett Evans is cited as a co-author.
Humans may not be native to Earth. Out in space they stumble on an alien fighting machine, and later make contact with perfect humanoid robots who acknowledge them as The Masters, returned.
There's even a character who says "Well, I've never been a proponent of genocide." But of course he goes on to make an exception for the current situation. I don't think Doc Smith was actually a big fan of genocide; he just kept looking for bigproblems to throw at his characters, and ultimately implacable menaces, and generally that ends up requiring their extinction.