On 20th February 1472, Orkney and Shetland officially became part of Scotland. The islands were offered up as security for the dowry of Princess Margaret, the prospective wife of James III of Scotland, and daughter of King Christian of Norway and Denmark.
In 1469, in an effort to subdue tensions between Scotland and Denmark, King James III was betrothed to Margaret of Denmark, daughter of Christian I, King of recently unified Denmark and Norway. A substantial dowry was arranged, but as Christian was a little short of money, first Orkney and then later Shetland were offered as protection in lieu of payment.
When it became clear that the dowry money was not forthcoming, the fate of the islands became inevitable. In 1470 the long-established title Norse Earl of Orkney was officially ceded to James III, and on 20th February 1472, both Orkney and Shetland officially became part of Scotland through an act of parliament.
Without the direct influence of Norwegian rule, the demographic profile of the islands gradually changed, and Scottish customs and culture superseded that of Norway. However, the islands have never quite lost their sense of Scandinavian heritage.
William Sinclair, 1st Earl of Caithness, was at that time the Norse Earl of Orkney. In 1472 he was made to exchange his Orkney fief for Ravenscraig Castle in Kirkcaldy.
James III (The Stewart Dynasty in Scotland), (2009), Norman Macdougall
Power and Propaganda: Scotland 1306-1488 (New History of Scotland), (2014), Katie Stevenson