The reasons for the rise and fall of Spain.

We are talking about the period from the end of the 15th to the end of the 16th century. The reasons for the flourishing were:

Successful completion of the Reconquista in 1492 and the creation of a strong army and navy.
the presence in Spain itself of rich deposits, for example, metals.
Influence in Catholic Europe, the Spaniards had about in Italy and on the territory of modern Belgium and the Netherlands.
The influx of gold from the Western Hemisphere, from Mexico and Peru, where the Spaniards conquered the Aztec and Inca states by the middle of the 16th century.

The reasons for the decline:

The slow development of bourgeois relations, the low role of the bourgeois in society, the high role of conservative elements – the nobility and clergy.
Unsuccessful suppression of the revolution in the Netherlands.
The surrender of positions in world trade to the Dutch and the British.