It was the most powerful state at that time, and it was made up of two kingdoms: Castile and Aragon. Castile was larger and wealthier, and Aragon had prospered during the Middle Ages because of its flourishing Mediterranean trade.  It became a federation of territories and it was greatly influenced by Mediterranean people and cultures.
In contrast to Spain, Portugal was a poor Atlantic state of mariners.
Political: Centralization and the Spanish Monarchy.
1469-Isabella of Castile married Ferdinand, heir to the throne of Aragon. Castilian policies were successfully implemented to create a relatively centralized monarchy. In Castile, the crown centralized the system of justice and made the municipalities more subservient. The Castilian dialect emerged as the language of Spain.
The Church: Fernado and Isabele and their successors were known as the Catholic kings because of their devotion to the church. They brought the Church, its privileges, and some of its income from tithes and the sale of indulgences under royal control.
The Spanish Inquisition interrogated and punished those accused of questioning Church doctrine. The Inquisition became a respected instrument of royal and Church authority.
In Castile, Ferdinand and Isabella stripped the Castilian nobles of some of their privileges and power while giving out titles and positions. (To keep them satisfied) In contrast, the territories of Catalonia and Valencia had nobles that resisted attempts to reduce their privileges; therefore most of their noble rights were left intact.  Nonetheless, because they feared a revolt of the lower classes, they became allies of the crown.
The rulers of Spain were not able to tamper with Catalonia’s traditionally less centralized constitutional traditions. Thus, the territories of Catalonia and Valencia maintained their political institutions, principally their:
Cortes(assembly) – which continued to limit the authority of the monarchy .
The Spanish monarchy therefore was less of a “new monarchy” than that of France because particularly strong institutional limits on its effective authority remained.
In Castile, disagreements between the monarchy and the Cortes were frequent during the middle decades of the sixteenth century. The Cortes excluded nobles and had representatives from on the governments of the most important cities/towns in Castile. (excluded everyone else)
The Castilian Cortes continued to refuse taxes to subsidize the monarchy for thirty-five years. This battle led to an inefficient royal economic device.
Economic: The Spanish Economy.
Spain’s colonial empire in the Americas contributed to its expanding economy.  The Spanish Empire contributed considerably to the sixteenth-century trading boom. Mexican gold helped finance the next wave of conquests.
In 1545, Spaniards discovered the rich silver mines of Potosi.
A new refining process helped Spain triple the silver resources of Europe to its own profit.
Spain shipped colonial products and Spanish woolens to France and the Italian