The Modern Kingdom of Spain emerged as a union of the Kingdoms of Galicia, Leon, Castille, and Aragon that parallel the conquest of Islamic Caliphates. Because Galicia and Leon have a long history of unions and dissolutions with each other and Castille starting from the eleventh century, many sources discussing Spain will focus on Castille prior to the marriage of Isabella of Castille with Ferdinand of Aragon in 1469, uniting the two crowns in 1474 (This will depend on what kind of material you're looking at though. Because I've focused on Mediterranean history I know much more about Aragon than I do about Castille.)

This is a map of Spain in 1210 outlining the four catholic Iberian kingdoms, while this is a map of Iberia in 1360, when Galicia and Leon were integrated into Castille, and the Islamic Caliphate was reduced to the area around Grenada. The Integration of Galicia-Leon into Castille in 1230 was a consequence of Alfonso of Leon marrying Berenguela of Castille, whose son Ferdinand forcibly integrated the two kingdoms after his father's death (Alfonso had preferred the kingdoms to remain separate, and had intended Leon and Castille to be ruled by his wife's daughters from a previous marriage). Galicia had flip-flopped between unions with Portugaul and Leon since the eleventh century, and had been in a union with Leon since the death of queen Urraca in 1126.

No. The Kingdoms of Galicia, Leon, Aragon, Castile and parts of the Catalan counties and Navarra make up what would become Spain. León for example retained its status as a Kingdom until the 1830's (although it was considered a part of the unified Spain from 1230). The internal political landscape of Spain was and to some degree still is very complex.