Charles I of England
Heir apparent

In 1613, Charles's sister Elizabeth married Frederick V, Elector Palatine, and moved to Heidelberg. In 1617, the Habsburg Archduke Ferdinand of Austria, a Catholic, was elected king of Bohemia. The next year, the Bohemians rebelled, defenestrating the Catholic governors. In August 1619, the Bohemian diet chose Frederick, who led the Protestant Union, as their monarch, while Ferdinand was elected Holy Roman Emperor in the imperial election. Frederick's acceptance of the Bohemian crown in defiance of the emperor marked the beginning of the turmoil that would develop into the Thirty Years' War. The conflict, originally confined to Bohemia, spiralled into a wider European war, which the English Parliament and public quickly grew to see as a polarised continental struggle between Catholics and Protestants. In 1620, King Frederick was defeated at the Battle of White Mountain near Prague and his hereditary lands in the Electoral Palatinate were invaded by a Habsburg force from the Spanish Netherlands. James, however, had been seeking marriage between Prince Charles and Ferdinand's niece, Infanta Maria Anna of Spain, and began to see the Spanish match as a possible diplomatic means of achieving peace in Europe.

Unfortunately for James, negotiation with Spain proved unpopular with both the public and James's court. The English Parliament was actively hostile towards Spain and Catholicism, and thus, when called by James in 1621, the members hoped for an enforcement of recusancy laws, a naval campaign against Spain, and a Protestant marriage for the Prince of Wales. James's Lord Chancellor, Francis Bacon, was impeached before the House of Lords for corruption. The impeachment was the first since 1459 without the king's official sanction in the form of a bill of attainder. The incident set an important precedent as the process of impeachment would later be used against Charles and his supporters the Duke of Buckingham, Archbishop William Laud, and the Earl of Strafford. James insisted that the House of Commons be concerned exclusively with domestic affairs, while the members protested that they had the privilege of free speech within the Commons' walls, demanding war with Spain and a Protestant princess of Wales. Like his father, Charles considered discussion of his marriage in the Commons impertinent and an infringement of his father's royal prerogative. In January 1622, James dissolved Parliament, angry at what he perceived as the members' impudence and intransigence.

Charles and Buckingham, James's favourite and a man who had great influence over the prince, travelled incognito to Spain in February 1623 to try to reach agreement on the long-pending Spanish match. The trip was an embarrassing failure. The infanta thought Charles little more than an infidel, and the Spanish at first demanded that he convert to Catholicism as a condition of the match. They insisted on toleration of Catholics in England and the repeal of the English penal laws, which Charles knew Parliament would not agree to, and that the infanta remain in Spain for a year after any wedding to ensure that England complied with all the treaty's terms. A personal quarrel erupted between Buckingham and the Count of Olivares, the Spanish chief minister, and so Charles conducted the ultimately futile negotiations personally. When he returned to London in October, without a bride and to a rapturous and relieved public welcome, he and Buckingham pushed the reluctant James to declare war on Spain.

With the encouragement of his Protestant advisers, James summoned the English Parliament in 1624 to request subsidies for a war. Charles and Buckingham supported the impeachment of the Lord Treasurer, Lionel Cranfield, 1st Earl of Middlesex, who opposed war on grounds of cost and quickly fell in much the same manner Bacon had. James told Buckingham he was a fool, and presciently warned Charles that he would live to regret the revival of impeachment as a parliamentary tool. An underfunded makeshift army under Ernst von Mansfeld set off to recover the Palatinate, but it was so poorly provisioned that it never advanced beyond the Dutch coast.

By 1624, the increasingly ill James was finding it difficult to control Parliament. By the time of his death in March 1625, Charles and Buckingham had already assumed de facto control of the kingdom.
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