Looking back in all of history Spain was quite the empire, up there with France and Great Britain. Now whenever I look at modern things like the UN security council for example, or just military power and WW1/2, Spain is largely irrelevant.

What happened? I do know of when their entire fleet was raped by England back in the day, but that seems more like one incident not a reason for full-on decline. Would really appreciate some interesting education on the matter here.