With the outbreak of war and the visit of prince Charles to Raglan there was a general rallying to the house of Raglan of its neighbours, among whom the house of Pembroke had lost caste by erratic politics and aloofness, while Worcester eschewed the court and lived patriarchially in their midst. Charles made him a marquess (2 Nov. 1642), promised him Pembroke's Monmouthshire estates (2 Dec. 1642), and appointed him (and after him, in 1646, his younger son lord Charles Somerset) governor of Raglan (20 July 1644), while he in return allowed his son to place the family fortune of some £24,000 a year at the king's service. But his son's schemes (see below), giving as they did solid ground for the old fear of an Irish landing in Wales, and revealed to the world after the capture of the king's baggage at Naseby, produced yet another revulsion of local feeling (especially among the Pembroke connection), as appeared when the king paid two extended, but unsuccessful, visits to Raglan (July and Sept. 1645) to recruit. Early in 1646 Raglan was closely besieged, Worcester as lord-lieutenant of the forces in Monmouthshire (9 Dec. 1645) organizing and privately financing the defence, with occasional sallies on Caerleon (26 Jan.) and other neighbouring Roundheadcentres. Having scornfully rejected calls to surrender from Thomas Morgan (1604-1679) (q.v.) in June, and Fairfax in August, Worcester ceded the castle to the latter on 17 Aug. on terms which, while protecting the garrison, left him to the mercy of the enemy. Already aged and ailing, he d. a prisoner c. 18 Dec. 1646, and was given a State burial (with Presbyterian rites) in the Beaufort chapel at Windsor. His chaplain, Thomas Bayly (q.v.), who attended him to the end, published in 1649 an account of disputations on religion between him and the king at Raglan under the title Certamen Religiosum, and in 1650 Worcesters Apothegms. Anthony Wood (Athen. Oxon., iii, 200) describes him as ‘a great compromiser, a wise man, and above all a person of great and sincere religion.’ Generally reputed (according to Clarendon) ‘the greatest Money'd Man of the Kingdom,’ he had large sums laid out on mortgage in the three counties of Brecknock, Carmarthen, and Pembroke, as well as gold and jewels concealed for the use of his grandson, the future duke of Beaufort (see below); his revenues were impounded by Parliament from 1645 to finance the Irish campaign and his town houses used for State purposes.

The authenticity of the alleged commission of 1 April 1644, empowering him to raise two armies of 10,000 each in Ireland (to land respectively in North and South Wales) and another of 6,000 on the Continent by negotiation with Catholic powers, with the title of earl of Glamorgan and the promise of further honours, is still sub judice (see Dodd, Studies in Stuart Wales, 90-99, and authorities cited, p. 92 n.), but the earldom was certainly conferred informally early in 1645, when he was instructed to negotiate with the Confederate Catholics. He and his brother lord John Somerset crossed to Ireland in June, when he speedily secured the promise of military help (treaties of 25 Aug., 3 Sept., and 20 Dec.) in return for concessions so wide that he was seized as a traitor by Ormonde (26 Dec.) and repudiated by Charles (29 Jan. 1646) after the terms had leaked out. On his release (21 Jan.) he tried to outbid Ormonde by working for Charles (who still kept in touch with him till July, 1646) with the papal legate, but gave up and left for Paris in March 1648. Parliament retorted with a decree of banishment (14 March 1649) and the inclusion of his estates in the Act of 1651 for the sale of delinquents’ lands, but with a proviso reserving to the heir on succession such as had not already been alienated (e.g. £1,700 worth, including Chepstow and Gower, voted to Cromwell — who in turn confirmed the leases held since 1648 by colonel Philip Jones (q.v.), and smaller grants made to Hugh Peters. Driven home by poverty in July 1652, Glamorgan was imprisoned in the Tower from 28 July till he was released on bail on 5 Oct. 1654, having meanwhile (26 July 1653) been granted by Cromwell a pension of £3 a week from the Raglan estates. After the Restoration his claim to the duchy of Somerset (in fulfilment of Charles I's supposed promise) was heard by a Lords’ committee (Sept. 1660), but dropped by him on the ground of his failure to fulfil the implicit conditions. He was more concerned about the state of his fortune, which he reckoned to have been depleted by nearly a million pounds through the losses of the interregnum and his unpaid exertions in Ireland and elsewhere, on top of the loans which the Crown failed to honour; nor did the hopeful essays as an inventor described in his Century of Inventions (written 1655, published 1663) save him from becoming a prey to duns during his last months. He d. suddenly in London on 8 April 1667, and was buried in Raglan church. Clarendon (no friendly witness) describes him as one ‘whose Person many Men lov'd, and very few hated.’

At home he was hotly opposed by John Arnold (q.v.) and Sir Trevor Williams (q.v.), who had local grievances over Wentwood forest (now exploited intensively by the marquess for iron smelting) and Chepstow garrison respectively; he removed Arnold and seven other opponents from the Monmouthshire bench in 1678 and had Williams included with twenty-four other Welsh magistrates in the Privy Council's purge of 1680. Arnold retorted by organizing the out-boroughs of Newport and Usk against his use of Monmouth as a pocket borough, and so unseating his son (on petition, 26 Nov. 1680) as borough member, Williams having ousted him from the county seat at the last election. Early in 1681 they joined Sir Rowland Gwynne (see under Gwynne of Llanelwedd) in pushing through the Commons an address for his banishment from court and council and promoting an abortive bill for ‘taking away Lord Worcester's Ludlow court for Wales’ as ‘too great a trust.’ Charles II retorted by making him duke of Beaufort (2 Dec. 1682), while the new duke silenced Williams and Arnold by obtaining heavy damages against them for ‘scandalum magnatum’ (Nov. 1683), and his son (now marquess of Worcester) won back the Monmouthshire seat and kept it till 1688. To consolidate his victory Beaufort made a viceregal tour of his presidency (14 July-21 Aug. 1684). James II renewed his presidency (28 March 1685), gave him a colonelcy of foot, and enlisted his services to prevent an outbreak of political faction in Denbighshire in March 1685, to hold Bristol against the duke of Monmouth the following June, and to rally Wales to the Declaration of Indulgence in 1687; but a meeting of local magnates summoned to Ludlow for the purpose in Oct. fell flat, and was followed by another purge of county benches and militias and municipal corporations. Despite concessions like the duke's cancelling of these dismissals (Sept. — Oct. 1688) and his advocacy of the calling of Parliament (Dec.), Wales failed in the end to back up his promise in Oct. to raise 10,000 men there against William of Orange, nor did he this time succeed in holding Bristol for James. Favouring a regency rather than the crown for William, he nevertheless took the oath to him belatedly as William III in March 1689, but he was superseded at Ludlow by the earl of Macclesfield, and what little part he took in the politics of the reign was largely in opposition. He d. at Badminton on 21 Jan. 1700, and was buried in the Beaufort chapel at Windsor. His eldest surviving son, CHARLES SOMERSET, 4th marquess of Worcester, after being deprived of his army commission in favour of his Roman Catholic cousin of Powis because he helped to draw up the Commons’ address of Nov. 1685, urging the removal of Roman Catholic officers (May 1687, Luttrell, Brief Relation, i, 403; C.J., ix, 756-9), had joined the prince of Orange early in Dec. 1688; he was killed in a coaching accident in Wales in July 1698, and the dukedom went to his son, HENRY SOMERSET (1684-1714), 2nd duke of Beaufort, a more advanced Tory who eschewed public life till the Tory reaction of 1710. His second son, CHARLES NOEL SOMERSET (1709-1756), 4th duke, was reputed a Jacobite, and sheltered his son-in-law Sir Watkin Williams Wynn after the collapse of the ‘Forty-five.’

Although the 1st duke's prestige throughout Wales was not repeated in his successors, the wide and increasing extent of their family lands and wealth ensured their continued influence in the south-east. The family has generally provided Monmouthshire, and often Brecknock as well, with lords-lieutenant, and the former county continuously from 1805-74 with Tory M.P.s, while the boroughs from 1799 to 1831 gave each successive heir his entrée to Parliament. In 1799, however, Newport — now developing commercially, and always less open than the other boroughs to ducal influence — with the help of Sir Charles Morgan of Tredegar (q.v.) successfully disputed the claim of the 5th duke (HENRY SOMERSET, 1744-1803) to possession of its wharf, while Monmouth itself threw over the municipal domination of the 6th duke, HENRY CHARLES SOMERSET (1766-1835), in 1818. A challenge to his son in the borough election to the Parliament of 1820 — memorable because John Frost (q.v.), the future Chartist, supported it — failed, but in 1831 the Beaufort interest in the boroughs was routed by the reform candidate, the future lord Llanover, who, although unseated on petition, was returned again next year. Under these two dukes the coal and iron on the Beaufort estates, which had brought in a steady revenue since the 17th cent., forged rapidly ahead. The 5th duke also extended his sway in Monmouthshire by buying the old Pembroke lordships of Usk and Trelech; but in 1901 the 9th duke, HENRY ADALBERT WELLINGTON FITZ ROY SOMERSET (1847-1924), sold the Raglan estate (excepting the castle) to the Crown and the manorial rights there to his kinsman, lord Raglan, grandson of FITZROY JAMES HENRY SOMERSET (1788-1855), 1st baron Raglan, youngest son of the 5th duke of Beaufort, and famous as a soldier who, having served under Wellington in the Peninsula and at Waterloo, m. his grand-niece, succeeded him as commander-in-chief, and led the British forces in the Crimea till his death in the field, 28 June 1855.