The reconquista, the carthaginian conquest of much of iberia, the grand catalan company, the spanish civil war and the preceding 50 years of republican agitation against traditional monarchist society, the individual histories of different ethno-cultural groups on the peninsula (Galicians have celtic origines, catalan, basques, castillians, etc). The long history of moslem presence and the cross pollination of culture as well as the occasional muslim or christian noble supporting the other side. the jews who went into hiding in the medieval ages and kept practicing in secret. so much so so much.

I'm sorry, but we can not unfortunately allow this question in our subreddit. If you have a specific question about Spanish history, you'd be more than welcome to ask. :) However, as your question stands right now, it's unfortunately too unspecific.