Answer:
The marriage of Ferdinand and Isabella.
Step-by-step explanation:
Throughout history, various states and a multitude of peoples settled their political institutions in the Iberian Peninsula. Given that some disappeared and others evolved, there is no historiographic consensus when specifying in what temporary moment the origin or foundation of Spain can be located as a country (nation or State), to the point that even the possibility of that such a moment can not be specified, because Spain is the result of an evolutionary process.
There are five main proposals to situate the moment from which one can speak of Spain as a country: the era of the Visigoth kingdoms; the union of Crowns from the Catholic Kings; the existence of a first common monarch, Carlos I; the organizational and political change that the centralism of Felipe V supposed; and the promulgation of the Constitution of Cádiz.