To stop someone from feeling angry. (Cambridge Dictionary)
To soothe or mollify especially by concessions: Appease. (Merriam – Webster)
If you placate someone, you do or say something to make them stop feeling angry. (Collins Dictionary)
Make (someone) less angry or hostile. (Oxford Dictionaries)
What’s the difference between appease, propitiate and placate?
Sudan Is Described as Trying to Placate the West.