Is it possible to add "s" at the end of the word "people" to make it plural? If so, what does it mean?
Sure. "A people" means something similar to "nation" or "ethnic grouping" - so you can say "the peoples of the world" to mean "all the different nationalities in the world".
As the spokesman of imperialism he came to share his prescriptions for preserving the current pattern of domination, exploitation and pillage of the peoples of the world. It was like an Alfred Hitchcock movie. I would even propose a title: “The Devil’s Recipe”.