Spain

Centralization in Spain began when a marriage between the rulers of Aragon and Castile which were in Spain took place.  The heir to the throne of Aragon was Princess Isabella.  The prince of Castile was Ferdinand.  These two heirs fell in love and married each other, combining both Castile and Aragon.  This was the first key of development of the centralization of Spain.

The Church and the Gregorian Reform

In the tenth- and eleventh- centuries, the Church become under what is known as Lay Control.  Lay Control is when authority takes control over some business, agency, etc.  In this case, the local lords controlled the Church.  This led the Church to become a part in the feudal system.  Then all of this signals Pope Leo IX to take a stand and do something.  Later in the eleventh-century, we then see St. Gregory VII, whom the Gregorian Reform was named after, in a fight with the emperor of Germany, Henry IV.  And finally, Christendom and its meaning.