Short answers, pulled from the story.
The Crown of Castile was formed in 1230 when Ferdinand III stepped onto the throne of León to claim a crown that had been his father's. He inherited Castile from his mother Queen Berengaria in 1217 and León from Alfonso IX in 1230.
John I permanently set the number of cities allowed to send representatives to include Burgos, Toledo, León, Sevilla, Córdoba, Murcia, Jaén, Zamora, Segovia, Ávila, Salamanca, Cuenca, Toro, Valladolid, Soria, Madrid and Guadalajara. Granada joined that list after its conquest in 1492.
Antonio de Nebrija published the first edition of the Grammar of the Castilian Language in 1492 under the Catholic Monarchs. This publication marked a significant shift as all public documents during Alfonso X's reign were written in Castilian instead of Latin.
The Revolt of the Comuneros broke out when Charles left Castile in 1520 and released Joanna claiming to support her as sole monarch. Los comuneros were defeated one year later in 1521 after which Parliament became merely consultative.
Charles II died without descendants in 1700 provoking War of the Spanish Succession where Philip of Bourbon won and imposed unification policies over Crown of Aragon supporters of their enemies. Nueva Planta decrees promulgated by Philip V in 1716 unified Crown of Aragon and Crown of Castile into Kingdom of Spain.