Players will get one Bronze Trophy or 10 GamerScore Points if the successfully achieve the Middle Earth: Shadow of Mordor No Power in Numbers Trophy/Achievement. You need to help a Captain survive a Recruitment Power Struggle, and then kill him and all his new recruits.
To get the Middle Earth: Shadow of Mordor No Power in Numbers Trophy/Achievement you must have the ability to command Uruks. You will be able to command the Uruks if you play Middle Earth: Shadow of Mordor till the end.
To get No Power in Numbers Trophy/Achievement you need to brand a Captain and command him to infiltrate a Warchief. Doing this may or may not randomly unlock a recruitment mission. YOu need to wait till the recruitment mission appears on the map.
Now all you have to do is defend your captain and kill other Uruks. Once you are done with completing the mission, get rid of the Captain and all his recruits.
For those who are still unclear about how to get the Middle Earth: Shadow of Mordor No Power in Numbers Trophy/Achievement checkout this video: