Adelaide, Countess of Soissons
Adelaide( died 1105), was sovereign Countess of Soissons from 1057 until 1105.
She was the daughter of Renaud I, Count of Soissons, and his wife, whose name is unknown, widow of Hilduin III, Count of Montdidier..
Adelaide became ruler of the County of Soissons upon the death of her father and brother, Guy II, Count of Soissons, in 1057.
Adelaide married William Busac, Count of Eu, grandson of Richard I, Duke of Normandy.
Adelaide and William had five children: William Busac became Count of Soissons," de jure uxoris", upon their marriage.
Robert of Bar, Count of Marle
Robert of Bar( 1390 – 25 October 1415) was Lord of Marle between 1397 and 1413, Count of Marle between 1413 and 1415 and Count of Soissons between 1412 and 1415.
He was the only child of Henry of Bar and Marie I de Coucy, Countess of Soissons.
His great- grandfather was Edward III.
Because his father was the eldest son of Robert I of Bar, Robert claimed the Duchy of Bar.
He only renounced his claims after a large financial compensation and the levation of Marle to a County.
In 1412 he also became Count of Soissons .<br>
Robert was one of the many French casualties at the Battle of Agincourt.
Robert married in 1409 Jeanne de Béthune, Viscountess of Meaux( d. 1450), daughter of Robert VIII de Béthune, Viscount of Meaux.
They had one child, a daughter:
Renaud II, Count of Soissons
Renaud II( died 1099), son of William Busac, Count of Eu and Soissons, and Adelaide, Countess of Soissons.
Count of Soissons.
It is unclear when Renaud assumed the countship of Soissons from his disgraced father.
The latter was stripped of the County of Eu in 1050 but it is unclear when he relinquished the countship of Soissons.
Alberic of Trois- Fontaines identifies Renaud in his" Chronicles" but little is known about his rule.
It is not known whether Renaud married or had any children.
Upon the death of Renaud, his brother John became the Count of Soissons.
John III, Count of Soissons
John III (d. before 8 October 1286), son of John II, Count of Soissons, and Marie de Chimay.
Count of Soissons and Seigneur of Chimay.
John inherited the countship of Soissons upon his father’s death in 1272.
John married Marguerite de Montfort, daughter of Amaury, Count of Montfort, and his wife Beatrix de Viennois.
John and Marguerite had five children:
John was succeeded as Count of Soissons by his son and namesake upon the former’s death.
Marie I de Coucy, Countess of Soissons
Marie I de Coucy (April 1366 – after 3 March 1405) was Dame de Coucy and d'Oisy, and Countess of Soissons from 1397.
She succeeded to the title of suo jure Countess of Soissons, on 18 February 1397, upon the death of her father, Enguerrand VII de Coucy.
In addition to her titles, she also owned numerous estates in North-Eastern France.
She was the wife of Henry of Bar, and the granddaughter of King Edward III of England and Philippa of Hainault.
Margaret, Countess of Soissons
Margaret (or Margaretha) of Soissons (died ca. 1350) was ruling Countess of Soissons in 1305-1344.
She was the only daughter of Hugh, Count of Soissons, and Johanna of Argies.
In 1306 she succeeded her father as Countess of Soissons.
Margaret was married to John of Beaumont, son of John II, Count of Holland.
Margaret and John had five children:
Upon their marriage, John became Count of Soissons, "jure uxoris".
Philippa de Coucy, Countess of Oxford
Philippa de Coucy, Countess of Oxford, Duchess of Ireland (before 18 April 1367 – October 1411) was a first cousin of King Richard II of England and the wife of his favourite, Robert de Vere, 9th Earl of Oxford, Marquess of Dublin, Duke of Ireland.
Nocher II, Count of Soissons
Nocher II( d. 1019), Count of Bar- sur- Aube, Count of Soissons.
He was the son of Nocher I, Count of Bar-sur- Aube.
Nocher ’s brother Beraud( d. 1052) was Bishop of Soissons.
Nocher became Count of Soissons, jure uxoris, upon his marriage to Adelise, Countess of Soissons.
Nocher and Adelisa had three children: Nocher ’s son and namesake became Count of Bar-sur- Aube upon his death, and the countship of Soissons reverted to his wife.
His son Renaud would eventually become the Count of Soissons.
Margaret of Soissons, Queen of Armenia
Marguerite of Soissons( died before 4 July 1381) was a Queen consort of Armenia by marriage to Leo V, King of Armenia.
She was a daughter of John of Soissons and Marie de Milmars.
Henry of Bar
Henry of Bar (c. 1362 – October 1397, in Treviso, Italy) was lord of Marle and the Marquis de Pont-à-Mousson.
He was the eldest son of Robert I of Bar and Marie of Valois.
Very early in his life, he was betrothed to Isabella of Lorraine, daughter of John I, Duke of Lorraine.
In 1374 he went to the court of his uncle King Charles V of France and was knighted at the coronation of king Charles VI of France, fighting in the Flanders campaign in 1383 and the Guelders campaign in 1388.
He then returned to Bar and governed it on behalf of his father, who was often immobilised by attacks of gout.
His betrothal was broken off and his fiancée instead married Enguerrand VII, Lord of Coucy (†1397).
In November 1384 Henry himself married Marie de Coucy, Countess of Soissons (1366–1405), daughter of Enguerrand VII Count of Soissons & Sire de Coucy, by his first wife Princess Isabella of England, eldest daughter of King Edward III.
Marie became Dame de Coucy et de Oisy following her father's death in 1397.
Henry had two children by Marie:
In 1396, Henry negotiated the neutrality of Gian Galeazzo Visconti, Duke of Milan, in dealings with the French protectorate in the republic of Gênes.
He then fought on the side of the Duke of Nevers in the crusade against the Ottoman Empire, being captured at the end of the Battle of Nicopolis on 25 September 1396.
He was taken prisoner and later ransomed, but died at the crusader's camp in Treviso after contracting the plague in Venice on his return trip.

Question: What is the cause of death of Marie I De Coucy, Countess Of Soissons's husband?
Answer: plague