Offhand I can't think of a single well-recorded real-life historical instance where this has ever worked.

"Befriending" by force? Well, post-WWII Japan worked out pretty well for the United States. As for dealing with would-be enemies by actually befriending them, Alexander Nevsky sucked up to the Mongols and ended up getting a much better deal for Russia than many of the other places the Mongols invaded.