William Cavendish, 1. Herzog von Newcastle First English Civil War
As tension increased, both Charles and Parliament tried to secure key ports and weapons; an attempt by Newcastle to capture Hull in July failed. When Charles formally declared war in August, Newcastle was given command of the four northern counties, largely because he was willing to pay for his own troops. In November 1642, he advanced into Yorkshire, raised the siege of York, and forced Lord Fairfax to retire after attacking him at Tadcaster.
Fighting continued during the winter, as Newcastle tried to secure a landing place for an arms convoy organised by Henrietta Maria, who was in the Dutch Republic purchasing weapons. He had insufficient troops to hold the entire area, and Parliamentary forces under Lord Fairfax and his son Sir Thomas, retained key towns like Hull, and Leeds. In late February 1643, a convoy with Henrietta Maria and weapons landed at Bridlington, and was escorted to Oxford. Combined with a victory at Adwalton Moor near Leeds in June, he was created 'Marquess of Newcastle-upon-Tyne'.
The 1643 Solemn League and Covenant had created a Committee of Both Kingdoms, which for the first time co-ordinated Parliamentary strategy in all three war zones, England, Scotland and Ireland. In February 1644, the Scots under Leven besieged Newcastle, closing the major import point for Royalist war supplies. They made little progress, with the Marquess-based nearby at Durham.
Two weeks later, the Earl of Manchester defeated a Royalist force at Selby. Newcastle had to leave Durham, and garrison York, which city was besieged by the Scots, Sir Thomas Fairfax, and Manchester's Army of the Eastern Association. In May, Prince Rupert left Shrewsbury, and marched north; on 29 June, he arrived at Knaresborough, 30 kilometres from York, to find he was faced by a superior force. Despite Newcastle's opposition, the largest battle of the war took place on 2 July, at Marston Moor. The result was a decisive Royalist defeat that lost them the North, while York surrendered on 16 July.
As a military commander, Lord Clarendon described Newcastle as "fit to be a general as a bishop". However, Marston Moor was fought against his advice, while he was also intelligent enough to understand his limits, and recruited reliable subordinates. After Marston Moor, Newcastle left England for Hamburg, accompanied by his two sons and his brother Charles; in April 1645, they moved to Paris, where he met and married his second wife Margaret, maid of honour to Queen Henrietta Maria. While there, Newcastle continued his feud with Prince Rupert, suggesting to the Queen he should be removed from command.
The new Marchioness was a dramatist and romancer, and had been maid of honour to Queen Henrietta Maria. Their marriage appears to have been a very happy one, and she later wrote a biography of him. His love and admiration for his wife is best expressed in the fine sonnet he wrote as an introduction to her masterpiece The Blazing World.
Newcastle left in 1648 for Rotterdam with the intention of joining the Prince of Wales in command of the rebellious navy, and finally took up his abode at Antwerp, where he remained till the Restoration. In April 1650 he was appointed a member of Charles II's privy council, and in opposition to Edward Hyde advocated the agreement with the Scots. In Antwerp he lived in the Rubenshuis (the house where the painter Peter Paul Rubens had lived from 1610 till his death in 1640) and established his famous riding-school, exercised "the art of manège" (High School riding), and published his first work on horsemanship, Méthode et invention nouvelle de dresser les chevaux in 1658. This work had an influence on one of the greatest French riding masters, François Robichon de La Guérinière, as well as a more controversial figure in dressage, Baucher. He is also said to be the inventor of draw reins.