Question:  John Stewart, Earl of Mar was the youngest son of an unpopular and ineffective what?

Context articles: Duke of Mar
John Stewart, 3rd Earl of Buchan
John Erskine, Earl of Mar (1675–1732)
James III of Scotland
John Stewart, 1st Earl of Traquair
Earl of Leitrim
John Stewart, Earl of Mar (d. 1479)
John Stewart, Earl of Mar (d. 1503)
John Stewart, 3rd Earl of Atholl
Lord Cardross

The Jacobite title of Duke of Mar was conferred on John Erskine, 6th/23rd Earl of Mar, by the Jacobite pretender James III and VIII.
 He was created "Duke of Mar", "Marquess Erskine" or "Marquess of Stirling", "Earl of Kildrummie", "Viscount of Garioch" and "Lord Alloa, Ferriton and Forrest" in the notional Peerage of Scotland in 1715, with the same remainder as his Earldom, i.e. to heirs-general.
 The Duke's attainder by the government of the Hanoverian George I the following year was, of course, not recognised in Jacobite circles.
 He was further created "Earl of Mar" in the Peerage of England in 1717 and "Duke of Mar" in the Peerage of Ireland in 1722.
 These titles had the ordinary remainder to heirs male of the body, and became extinct on the death of the grantee's son in 1766.
 The other titles, such as they are, remain extant, although they are not recognised by the British or any other government and have not been claimed or used by their holders since the eighteenth century.
John Stewart, 3rd Earl of Buchan, son and heir of Alexander, succeeded to the Earldom in 1505.
 He was retoured heir to his father in the Earldom and Earlshill in 1519; until then he retained the style of Master of Buchan which he had held in his father's lifetime.
 On his own resignation, a charter of all his lands, baronies, lordships, and heritable offices, and of the Earlshill, was granted 4 August 1547 to his son John Stewart and his heirs, reserving the Earl's liferent.
John Erskine, Earl of Mar, KT (1675 – May 1732), Scottish Jacobite, was the eldest son of Charles, Earl of Mar (who died in 1689), from whom he inherited estates that were heavily loaded with debt.
 He was the 23rd Earl of Mar in the first creation of the earldom.
 He was also the sixth earl in the seventh creation (of 1565).
 Other sources count him as 22nd earl, still others number him 11th earl (See notes).
 He was nicknamed "Bobbing John", for his tendency to shift back and forth from faction to faction, whether from Tory to Whig or Hanoverian to Jacobite.
 Deprived of office by the new king in 1714, Mar raised the standard of rebellion against the Hanoverians; at the battle of Sheriffmuir in November 1715, Mar's forces outnumbered those of his opponent, but victory eluded him.
 At Fetteresso his cause was lost, and Mar fled to France, where he would spend the remainder of his life.
 The parliament passed a Writ of Attainder for treason against Mar in 1716, as punishment for his disloyalty, which was not lifted until 1824.
 He died in 1732.
James III (10 July 1451/May 1452 – 11 June 1488) was King of Scots from 1460 to 1488.
 James was an unpopular and ineffective monarch owing to an unwillingness to administer justice fairly, a policy of pursuing alliance with the Kingdom of England, and a disastrous relationship with nearly all his extended family.
 However, it was through his marriage to Margaret of Denmark that the Orkney and Shetland islands became Scottish.
John Stewart, 1st Earl of Traquair (died 27 March 1659) was a Scottish statesman, the son of John Stewart, the younger, of Traquair in Peeblesshire, of a branch, originally illegitimate, of the house of Buchan, and was created Baron Stewart of Traquair in 1628 and earl of Traquair in 1633.
Earl of Leitrim (pronounced "Leetrim") was a title in the Peerage of Ireland.
 It was created in 1795 for Robert Clements, 1st Viscount Leitrim.
 He had already been created Baron Leitrim, of Manor Hamilton in the County of Leitrim, in 1783, and Viscount Leitrim in 1793, also in the Peerage of Ireland.
 In 1800 he was elected as one of the 28 original Irish Representative Peers.
 Lord Leitrim was the son of the influential politician and financier Nathaniel Clements.
 He was succeeded by his son, the second Earl.
 He was created Baron Clements, of Kilmacrenan in the County of Donegal, in the Peerage of the United Kingdom in 1831, which gave him and his descendants an automatic seat in the House of Lords.
 His eldest son Robert Clements, Viscount Clements, represented County Leitrim in Parliament.
 However, he predeceased his father, unmarried.
 Lord Leitrim was succeeded by his second son, the third Earl.
 He also sat as Member of Parliament for County Leitrim.
 A deeply unpopular landlord,Lord Leitirim was instructed to arm himself for protection and to be in the company of a strong bodyguard.
 Lord Leitrim was murdered along with his clerk and driver by three men named Neil Shiels, Michael Mc Elwee and Michael Heragty while on his way to his residence in Milford in 1878.
He was unmarried and was succeeded by his nephew, the fourth Earl.
 He was the son of the Reverend the Hon. Francis Nathanial Clements, fifth and youngest son of the second Earl.
 Lord Leitrim served in the Royal Navy.
 He was succeeded by his eldest son, the fifth Earl.
 He served as Lord-Lieutenant of the City of Londonderry.
 He was twice married but childless.
 As Lord Leitrim's two younger brothers had both died unmarried before him the titles became extinct on his death in 1952.
John Stewart, Earl of Mar and Garioch (c. 1456–c. 1479) was the youngest surviving son of James II of Scotland and Mary of Guelders.
John Stewart, Earl of Mar (December 1479 – 11 March 1503) was the youngest son of James III of Scotland and Margaret of Denmark.
John Stewart, 3rd Earl of Atholl (1507-1542) was the son of John Stewart, 2nd Earl of Atholl and Lady Janet Campbell, a daughter of Archibald Campbell, 2nd Earl of Argyll and Elizabeth Stuart.
Lord Cardross is a title in the Peerage of Scotland, since 1695 a subsidiary title of the earldom of Buchan.
 It was created in 1606 for John Erskine, 18th Earl of Mar, with remainder to his heirs male and assignees whatsoever and with the power to nominate his successor.
 In 1617 he nominated his second son by his second wife, Henry Erskine, Master of Cardross, to be his successor in the lordship of Cardross.
 The Earl of Mar died in 1634 and was succeeded in the earldom of Mar by his son by his first wife, John, and in the lordship of Cardross by his grandson David Erskine, the second Lord Cardross, the son of Henry, Master of Cardross, who had died in 1628.
 The second Lord was a supporter of The Engagement and was barred from sitting in Parliament in 1649.
 He was succeeded by his eldest son, the third Lord.
 He emigrated to North America to escape religious persecution and established a colony in what is now Carolina.
 His son, the fourth Lord, succeeded his kinsman in the earldom of Buchan in 1695.
 However, it was not until 1698 that his claim was established by the Scottish Parliament.
 For further history of the title, see Earl of Buchan.