You are talking about large empires, and, indeed, I agree with all. But there are some tiny countries that provoke amazement by the sheer luck by which they remained sovereign through various centuries.
I guess some people won't agree, but I think Switzerland is fairly bizarre. If you pick an (historically) uneducated person, point that tiny country wedged between France, Germany and Italy, you'd already get a confused stare by the sheer disproportion. Even before Germany, there were France and Austria, and southern German principalities with a larger manpower base and wealth to tackle on this Alpine country. Now, the Swiss have a very defensive geography, of course, but the political history of the country is another thing that amazes me: it was amalgamation of former feudal provinces into a genuine confederation (in which every constituent part is a sovereign state) that formed a republic unlike the model of the Italian and Hanseatic merchant republics (a "modern" republic, it seems, like the Netherlands), with no common language. I mean, all it took would be a determined conqueror to wipe Switzerland off the map - like France did during the Revolution - or even to simply break it up for its neighbors to eat its cantons one by one - like what happened to Poland - but it still managed to survive and eventually grew to be one of the richest countries in the world by being peaceful and landlocked.
The same applies to San Marino, I suppose.