Why Are Openings Named After Countries? This has been bothering me from when I was little. Why are openings most commonly named after a country? For example: Sicilian, Scotch, Spanish, etc...
There's a variety of reasons why openings are commonly named after nations (but most commonly would surprise me), maybe due to an individual player of the nation, e.g. Spanish (Ruy Lopez), English (Staunton), maybe due to a group of players in one nation e.g. Italian, maybe due to an event involving the nation e.g. Scotch (named for a correspondence match between Edinburgh and London in the 1800s), and I suspect a number of other reasons, including "we don't really know"

Wikipedia list of chess openings named after places might be a good place to start researching this