To earn the trophy that's called "Divide And Conquer", you must first kill the bodyguards of two different Warchiefs, then draw out those Warchiefs and kill them as well.
Load up Sauron's Map and look at all five Warchiefs. One of those Warchiefs should have a blue line going straight towards a Captain. That blue line means that the Captain is a bodyguard to that Warchief. To make this trophy easier, try going after a Warchief that has at least one or two bodyguards with him. Do the same with the other Warchief and take note of their mental locations.
From there, hunt down those specific bodyguards for those two Warchiefs and kill them. Once that's accomplished, head on over to the location where the Warchief can be found. Then do the mission to draw him out before eliminating him, then do the same thing for the other Warchief as well.
Another alternative way of doing this is finding a Warchief with his bodyguards, then draw out the Warchief so that you can destroy his bodyguards first before killing the Warchief before moving on to the next Warchief with his bodyguards. That's what I did to get the trophy faster, so I've written for you, the player, at least two ways to get this trophy.
If you need a video attachment to help you understand further on how to get this trophy unlocked, I can aid you in this regard as well. All credit goes to Game Boys of Colour for the video. Happy hunting, have fun, and good luck!