THE REIGN OF THE CATHOLIC MONARCHS (I)
THE DYNANSTIC UNION OF CASTILLA AND ARAGON
DOMESTIC REFORMS
At the end of the 15th century
The Catholic Monarchs made some domestic reforms to centralise power
Such as
Reform the existing institutions
Establish new institutions
Increase the number of royal officials
They made this reforms to achieve 4 objectives
To weaken the power of the nobility
The Council of Military orders managed military orders and the Council of the Supreme Inquisition managed moral and faith issues
Trained officials replaced nobles in institutions like the Council of Castilla
Which the Pope's permission, they placed Military Orders under their control
They formed an army of mercenaries to overpower the militias of the nobility 
The royal treasury had more power to control tax collection
Councils of experts advised monarch about
To reduce the autonomy of the kingdoms of the Hispanic Monarchy
They reduced the power of the General Courts
They selected viceroys, who represented them in each kingdom in their absence
The Inquisition was established to persecute false conversos
To restrict the autonomy of the urban oligarchies
In Castilla, the monarchs chose who the mayor was
In Aragon, the sortition system was maintained. Which means that the mayor was chosen by lottery. 
To improve international relations
The diplomatic corps, which represented the monarch in other kingdoms, was expanded
The audiencias of Valladolid and Granada restructured the judicial system
A militia, the Santa Hermandad, was created to keep peace in Castilla
Castilla was a more authoritarian monarchy than Aragon because there the pact tradition was maintained, which means that the king made decisions with approval of the regional institutions
Isabella and Ferdinand established and authoritarian monarchy on the Iberian Peninisula
Other authoritarian monarchies were established in England and France
In 1469, Isabella and Ferdinand got married
When the King of Castilla died in 1474, a civil war started between
Joanna la Beltraneja, who had the support of Portugal
Isabella, who had the support of Aragon, and finally won in 1479 
In 1479, Isabella and Ferdinand formed the dynastic union of Castilla and Aragon because that year Ferdinand also became king
This union didn't result in the creation of a unitary state as each kingdom retained its own institutions, laws, language...