The map is the frame, not the background
Almost every high-performing thumbnail in this niche is map-first: a region shown at a scale that makes the geography itself the argument. Two countries with a border between them, a strait pinched between landmasses, a supply route drawn across an ocean. The map communicates the stakes without a single word, and it's the fastest way to say 'this video explains something' rather than 'this video reports something'.