Euskera
Euskadi is the name the former Basque Country has now.
I actually mixed two dates, which I often do, sorry. It’s 1841.
1492: Conquest of Granada by Castilla. Granada becomes a part of Castilla.
1517: Conquest of the lower Navarra by Aragonese troops, ending (sort of) the hereditary mess caused by the overgrabiness of Juan II of Aragon, husband of Blanca I of Navarra. Ferdinand I of Aragon, husband of Isabel I of Castilla, is proclaimed king of (the lower) Navarra as well as already being king of Aragon. The two kingdoms remain independant, though; also, the upper Navarra (the SW corner of France) is in the hands of the French king, who is a descendant of Navarra-born Henri II and whose claim to the Navarrese throne is actually more legitimate than that of Fernando (who is not related by blood to Blanca at all, he was a child of Juan II’s second marriage; the original heir, Carlos, Príncipe de Viana, son of Juan and Blanca, was murdered by Juan - who needs soap operas when you have the Trastamaras?; Carlos’ sister, Blanca the Youngest, was the first wife of Isabel’s uncle, bastard-born Castillian king Enrique de Trastamara “he who could not get it up” according to the divorce proceedings from said Blanca, who’d gained the throne by beating his legitimate brother Pedro II the Cruel)
For the next two centuries the French and Spaniards spend more than a summer raiding across the Pyrinees, but it’s generally small raids which most history books don’t ever mention.
Carlos I of Castille, I of Aragon, IV or V of Navarre (depending on whether you count his great-half-uncle or not) is king of all three kingdoms, but each kingdom keeps its own Parliament, Laws and Customs. This situation remains through the Habsburg reign.
c. 1700, the last Habsburg dies without issue. An Englishman is the closest heir for Aragon; a Frenchman for Navarra; Castilla has no clear heir, but there is a part of Castilla (the Vascongadas… nowadays, Euskadi) which pressures to help the French candidate, and wins Castillian allegiance for him. After some smacking of heads, the french Philip V, grandson of Louis XIV, wins. He declares Aragon “conquered land”, dissolving their Parliaments, all local and, uhm, kingdom-wide laws, imposing Castillian laws, taxation… People from the Crown of Aragon are nooooot particularly fond of him, for some reason.
He would have liked to do the same with the Vascongadas (which for many things had their own local laws, separate from those of Castilla and more similar to those of Navarra) and to Navarra, but since there was no way he could declare those “conquered lands”, he just had to suck and grunt. The expression “Contrafuero: se obedece pero no se cumple”, which my Catalan mother claims is a perfect explanation of many Navarrese peculiarities, is from this period: the king kept sending orders that went against our Law and Tradition (Fuero), so the Diputación Foral (the group of 7 “deputies” which represented Parliament when it was not in season) kept writing back: “Against the Law: we obey your majesty, but we can not do as you order.”
Also from this period are two groups of Probanzas de Sangre; another tack that Philip tried in order to subdue the Diputaciones of Navarra, Álava, Vizcaya and Guipúzcoa was by claiming that those “stubborn” deputies did not have the right to sit in Parliament, therefore did not have the right to be Deputies. So everybody from those areas who claimed a right to sit in Parliament had to go and prove that they had the bloodright.
Both the Habsburgs and the Borbones avoided calling the Navarrese Parliament into season or visiting the Diputaciones of either location, but the Diputaciones had mechanisms to continue indefinitely. So the kings could dance jotas on a pin if they wanted, our Diputados would just inform them when they missed a step 
Early XIX century, Napoleonic invasion, restoration of the Borbones. Fernando VII “the wished for” is, in my I’m-not-a-historian’s opinion, one of the worst kings any of our kingdoms ever had. He kept swinging from far left to far right and back, always without any regard for such niceties as Law, Tradition and Proper Procedure. He didn’t try to fight the Diputaciones; he just did his best to ignore them. One of the things in which he completely disregarded his own laws was the naming of his heir, which was the excuse for the First Carlista War (my Carlista relatives count the Civil War of 1936 as being the Sixth Carlista War).
1841 is the year of the Ley Paccionada, the “tratado de hermandad” by which Castilla and Navarra become a single kingdom, “keeping each of the two parts its own Laws, Customs and Parliament.” We got rid of the official border between both kingdoms (still, it’s the same line followed by the present-day Province of Navarra), of the Navarrese mint, and little more. The Estatua de los Fueros, at the foot of Paseo Sarasate in Pamplona, celebrates both this Brotherhood Treaty and the Gamazada, the 1894 rebellion defending it (when, once more and we’re in 2007 and they still do it, Madrid tried to force our Diputación to copy their taxation system; nowadays we just throw the lawyers at them and they end up having to pay judicial costs as well as lick their wounds).