Did Spanish have declensions?

Question

Since Spanish evolved from Latin, and Latin has cases (Nominative, Acusative, Dative, Genitive, Ablative) did Spanish nouns change, sometime ago, with respect to cases?

Answer 1

Case was already disappearing by Popular Latin in favor of prepositions. One of the earliest sound changes from Latin into Romance was the loss of final m, which was a prominent case marker. By the 400s, Popular Latin had already been reduced to two cases: a nominative and non-nominative. When Spanish emerged as its own language, it took the accusative (non-nominative) form as its base form. This also explains Spanish plurals: We form them with an -s, as was true of the non-nominative nouns, whereas Italian, which took its nouns from the nominative, forms plurals by changing the last vowel. So no, Spanish never had case; they all merged or disappeared before the seventh century, which is about when the distinct Romance varieties are believed to have fully formed.

If you want to read more, try these two sources. (My answer draws from the first)

1. Alkire, T., & Rosen, C. (2010). Romance languages a historical introduction. Cambridge: Cambridge University Press. (Specifically, Chapter 8)
2. Penny, R. (2009). A history of the Spanish language. Cambridge: Cambridge Univ. Press.