I was walking to our fave lunch spot today and out of my random thoughts (as usual), I've never really figured out back in elementary as to why we refer to Spaniards as "mga Kastila".

There's a more helpful word for Spaniards which is Espanyol (better eh?). But what's Kastila then?

The answer lies on Spanish history on that there existed the Kingdom of Castille, a historical kingdom from the 9th to the 13th century. Or perhaps from Old Castile, the political name of the region formed by Santander, Burgos, Logroño, Soria, Segovia, Ávila, Valladolid and Palencia. It had some territorial changes in its History, and had this name from 18th century to 1983.

Though from looking at the timeline, we could say Kastila came more from the kingdom than from the political party.