@SaintDaveUK There's a fair bit academically regarding the island, for the most part it was independent until 1399, however the history behind it is a bit odd and it could even be interpreted as a condominium between Scotland and England. Tim Thornton noted in 1998 that the island was Scottish in 1328, just 9 years before the start date (Thornton, 1998).
"Equally, during periods of weakness, the English unequivocally accepted not only that the Isle of Man was Scottish, but, as in 1328, that it was subject to the Scottish king."
Edward III granted the island to William de Montacute 1st Earl of Salisbury prior to the second Scottish War of Independence, this was seen as an English de jure legal transition away from Scottish rule to independence for the Isle of Man.
"In the case of Man, Edward's grant of the island to William de Montacute, grandson of the heiress Auffricia de Connaught, and the terms in which it was made, seem in some ways to have resolved the question of Man's position in terms of a shift away from Scotland back to greater independence."
However in May of 1333, Edward III took the isle of Man by force during the Second Scottish war of Independence, thus cementing a de facto wrestling out of Scottish hands in addition to the aforementioned de jure legal transition.
"On 30 May 1333 Edward took control of the island: stating that Edward I had been legitimately seized of Man, he implied that he did not recognise the sovereignty exercised there by either John Balliol or the Bruces."
What we do know is that Edward III quitclaimed (renounced his claim) to the island on behalf of the Plantagenet dynasty in August of 1333, handing full suzerainty to William de Montacute, who would go on to rule the Kingdom of Man independently whilst also sitting in the parliament of Scotland and a subject to the English crown via his lands within England but also an independent King of Man. Here is the renunciation of Edward III's claim in full.
"That did not, however, mean the end of the Scottish connection. Montacute was present as ruler of Man in the Scottish Parliament which ratified the Roxburgh agreement with Balliol"
"The island was permitted an unusual and specific relationship with the Scots, for example in the permission given by William de Montacute and confirmed by the king in 1342 for the men of Man to pay an indemnity of 300 marks to the Scots for a one-year"
When the Montagu line died out when William Montagu, 2nd Earl of Salisbury passed away in 1397, it's ownership passed to William Scrope, 1st Earl of Wiltshire. Upon the rebellion of Henry Bollingbroke (Henry IV), Scrope supported Richard II, and thus, when Henry IV won the war, Scrope as an English landowner was put to death and his lands inherited into the crown, thus signaling the end of the independent Kingdom of Mann in 1399, one year before Glyndwr's revolt.
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I learnt this as part of studying for my project on the Welsh War of Independence, was very interesting, mainly because the lands were therein given to Henry Hotspur, who went on to ally with Glyndwr during the war of independence after 1403 onwards and was a signature of the tripartite indenture in 1405, attempting to split the Kingdom of England between himself in Northumbria, Glyndwr in a now far larger Wales and Mortimer in the rump state of England.
Maybe the Kingdom of Mann could be a vassal of England up until 1399, as a game mechanic, Mann remains a vassal now under the ownership of Henry Percy (Hotspur), who alongside Glyndwr and Mortimer, signed the Tripartite Indenture. The isle of Mann after 1399 could then act as a base for Hotspurs forces during Glyndwrs war of Independence, where he would then attempt annex what is now Northumbria. When this fails, the Kingdom of England should inherit the Isle of Mann via event signaling the end of the rebellion.
View attachment 1149770
The map of the proposed division of England between Glyndwr, Mortimer and Hotspur as per the tripartite Indenture for my current project.
Thornton, T. (1998). Scotland and the Isle of Man, c. 1400–1625: noble power and royal presumption in the Northern Irish Sea province. Scottish Historical Review, 77(1), 1-30.
