[1] The Thirty Years War began in 1618 when the Protestant-dominated Bohemian Estates offered the Crown of Bohemia to Frederick of the Palatinate, rather than Holy Roman Emperor Ferdinand II, a Catholic.

However, with neither Ferdinand nor Frederick prepared to back down, Imperial forces invaded the Palatinate; removal of a hereditary prince changed the nature and extent of the war.

[3] Protestant states within the Empire saw it as a threat, including external powers who held Imperial territories; Nassau-Dillenburg was a hereditary possession of the Dutch Prince of Orange, while Christian IV of Denmark was also Duke of Holstein.

This escalation coincided with the end of the Twelve Years' Truce between the Dutch Republic and Spain, and provided an opportunity for the Kingdom of France, which faced a series of Spanish-backed Huguenot rebellions.

[8] In 1620 the Spanish commander Don Ambrosio Spinola adopted Fabian strategy,[3] in the hope of wearing the enemy out, until the approach of winter compelled the English and their allies to seek quarters.

[18] In March, Johann Tserclaes, Count of Tilly, and the army of the Catholic League invaded from Bavaria;[3] Meanwhile, The garrison under Sir Horace Vere at Mannheim received a visit early in 1622 from the dethroned Frederick, who had promised them a diversion.

[citation needed] Meanwhile, after his defeat in Hochst, Frederick cancelled the contract of the protestant forces under his lead, which they were then hired by the Dutch Republic to lift the siege of Bergen-op-Zoom.

[29] On 6 August, Tilly defeated a Protestant army under Christian of Brunswick in the Battle of Stadtlohn, and Frederick signed an armistice with Ferdinand, ending the "Palatine Phase" of the Thirty Years' War.

[30] In recognition of his service during the Palatine conflict, Horrace Vere was appointed Master-General of the Ordnance for life On 16 February 1623, and he became a member of the Council of War on 20 July 1624.

[3] C. V. Wedgwood consider the Spanish and Dutch involvement in the campaign was a significant step in internationalising the war, while the removal of Frederick V from title prompts other Protestant princes began discussing armed resistance to preserve their own rights and territories.