I want to design a geopolitical game like Rival Region what are the resources I would need.

Gimp or Photoshop for 2D art. Blender, 3DsMax or Maya for 3D art. 

Unity, Godot or Unreal for a game engine. Learn what programming your engine uses.

If you are new I recommend: Gimp, Blender and Unity. These are all free (Unity has terms) and high quality tools.