From Imperial Spain: 1469-1716, by J. H. Elliott (Penguin, 2002), 2nd ed., Kindle Loc. 2489-2536:
The new King, a gawky, unprepossessing youth with an absurdly pronounced jaw, did not make a favourable impression on his first appearance in Spain. Apart from looking like an idiot, he suffered from the unforgivable defect of knowing no Castilian. In addition, he was totally ignorant of Spanish affairs, and was surrounded by an entourage of rapacious Flemings. It was natural to contrast him un-favourably with his brother Ferdinand, who enjoyed the supreme advantage of a Castilian upbringing – a background that seemed to Charles’s advisers to be so fraught with danger for the future that they shipped Ferdinand off to Flanders a few months after his brother’s arrival in Spain. His departure, which (as was intended) deprived the grandees of a potential figurehead and the populace of a symbol, merely increased the discontents of a disaffected nation.
The principal complaint of the Castilians was directed against the Flemings, who were alleged to be plundering the country so fortuitously inherited by their duke….
When the Cortes were held at Valladolid in January 1518 to swear allegiance to the new King and vote him a servicio, the procuradores seized the opportunity to protest against the exploitation of Castile by foreigners; and they found some outlet for their indignation in addressing Charles only as ‘su Alteza’, reserving the title of ‘Magestad’ exclusively for his mother, Juana….
News reached Charles as he was on the road to Barcelona at the end of January 1519 of the death of his grandfather Maximilian; five months later, after long intrigues and the expenditure of vast sums of money, he was elected Emperor in his grandfather’s place. Gattinara, a man whose broad imperial vision was inspired by a cosmopolitan background, an acquaintance with the political writings of Dante, and, most of all, by the humanist’s longings for a respublica christiana, showed himself fully prepared for the change. Charles was no longer to be styled ‘su Alteza’, but ‘S.C.C.R. Magestad’ (Sacra, Cesárea, Católica, Real Magestad). The Duke of Burgundy, King of Castile and León, King of Aragon and Count of Barcelona, had now added to his imposing list of titles the most impressive of all: Emperor-elect of the Holy Roman Empire.
Charles’s election as Emperor inevitably altered his relationship to his Spanish subjects. It did much to increase his prestige, opening up new and unexpected horizons, of which the Catalans – as a result of his residence among them at this moment – were probably the first to become aware. Charles himself was changing, and beginning at last to acquire a personality of his own; he seems to have established an easier relationship with his Catalan subjects than with the tightly suspicious Castilians; and Barcelona for a glorious six months revelled in its position as the capital of the Empire.
If a foreign ruler had obvious disadvantages, there might none the less be compensations, as yet barely glimpsed. It was the disadvantages, however, which most impressed the Castilians as Charles hurried back across Castile in January 1520 to embark for England and Germany. If the King of Castile were also to be Holy Roman Emperor, this was likely to lead to two serious consequences for Castile. It would involve long periods of royal absenteeism, and it would also involve a higher rate of taxation in order to finance the King’s increased expenditure. Already, at the news of Charles’s election, voices were raised in protest against his impending departure. The protests originated in the city of Toledo, which was to play the leading part in the troubles of the next two years, for reasons that are not yet fully clear. The city seems somehow to have exemplified, in heightened form, all the tensions and conflicts within Castile, offering an illuminating example of the constant interaction of local and national affairs.