I've always kind of wondered this, but when and why did Spain decline in power and influence so much. Up until around the 1600s Spain was one of, if not the, wealthiest, most powerful, and most influential countries in the world. But since then it's been something of a footnote. The Spanish-American war barely is covered in school and Franco's Spain is something of a side note to the rest of what's going on at the time. And today, you hardly hear anything about Spain. France, Britain and Germany seem to have all the influence in Europe.
I should note that I am American, so maybe Spanish history is more well known outside. But here, after the defeat of the Spanish Armada, Spain's contribution to world history seems to be shrugged off
History is, of course, never monocausal, and there will be a great deal more to be said in response to such a complex question. But one factor, certainly, was Spain's handling of its finances, which I addressed in this recent response:
How did Spain go bankrupt 9 times between 1557 and 1666 and what were the actual effects of that?
You might like to review that thread while waiting for fresh responses to your query.