What was the reason for spains rise and fall?

During the 15th and 16th centuries Spain was the most powerful country because of the discovery of America and gold and silver, the union of Castile and Aragon under Ferdinand and Isabella, religious unification, the conquering of Granada, and an age of new learning. The was called Spain's "Golden Age". One of the main reasons for Spain's fall is because the Spanish empire was too large to control.