The Spanish language developed from vulgar Latin, with influence from Celtiberian, Basque and Arabic, in the north of the Iberian Peninsula. Typical features of Spanish diachronical phonology include lenition (Latin vita, Spanish vida), palatalization (Latin annum, Spanish año) and diphthongation (stem-changing) of breve E/O from vulgar Latin (Latin terra, Spanish tierra; Latin novus, Spanish nuevo). Similar phenomena can be found in most other Romance languages as well.
During the Reconquista, this northern dialect was carried south, and indeed is still a minority language in northern Morocco.
The first Latin to Spanish dictionary (Gramática de la Lengua Castellana) was written in Salamanca, Spain in 1492 by Elio Antonio de Nebrija. When Isabella of Castile was presented with the book, she asked, What do I want a job like this for, if I already know the language?, to which he replied, Ma'am, the language is the instrument of the Empire.
From the 16th century on, the language was brought to the Americas, Federated States of Micronesia, Guam, Marianas, Palau and the Philippines, by Spanish colonization.
In the 20th century, Spanish was introduced in Equatorial Guinea and Western Sahara.