Geography. There’s no doubt: knowing history or other contextual information makes it much easier to remember. If you’re starting from scratch with no prior knowledge, and all you need to do is know every capital of every country, I can’t imagine you could do it in less time than 5 minutes over a lifetime per country with anything other than spaced repetition. Maybe SketchyMicro could, if they really built an amazing memory palace of all the countries, maybe you wouldn’t need spaced repetition to recall that information for the rest of your life. Also, even if spaced repetition solves the brittle nature of remembering cognitively isolated information technically, relying on an external tool to maintain your memory is a different type of brittle, and an interesting discussion in itself.