West Iberian is a branch of the Romance languages that includes Castilian (Spanish and Judaeo-Spanish/Ladino), Astur-Leonese (Asturian, Extremaduran, Leonese, Mirandese and Cantabrian), and the modern descendants of Galician-Portuguese (Galician, Portuguese, and the Fala language). According to historical linguistic analysis, these languages are significantly closer to each other in historical terms than to any other living language in the peninsula—including Catalan, the other major Romance language of the Iberian Peninsula.
Until a few centuries ago, they formed a dialect continuum covering the western, central and southern parts of the Iberian Peninsula—excepting the Basque and Catalan-speaking territories. This is still the situation in a few regions, particularly in the northern part of the peninsula, but due to the differing sociopolitical histories of these languages (independence of Portugal since the early 12th century, unification of Spain in the late 15th century under the Catholic Monarchs, who privileged Castilian over the other Iberian languages), Spanish and Portuguese have tended to overtake and to a large extent absorb their sister languages while they kept diverging from each other.
There is controversy over whether the members of the modern Galician-Portuguese and Astur-Leonese subgroups are languages or dialects. A common, though disputed, classification is to state that Portuguese and Galician are separate languages, as are Asturian, Leonese, and Mirandese. Cantabrian and Extremaduran are considered codialects of the Leonese language for UNESCO, whereas the latter is a Castilian dialect in the ISO codes.