Margaret Maid of Norway
Annals Britannica mentions one of history's great what if? questions which concerns Margaret the Maid of Norway, who was the sole remaining heir to the Scottish throne when her grandfather died in 1286. She was three years old and her father, the king of Norway, arranged that she would marry the five year old Edward of Caernarfon, son and heir of Edward I, known as Longshanks, king of England, who would be Margaret's guardian during her childhood. The leading Scottish nobles, riven by deep divisions between the leading magnates, agreed to the marriage, so long as Scotland should remain free and separate from the kingdom of England. Four years later the Maid died in Orkney on her way to be crowned at Scone, Scotland.
The chief men of Scotland asked Edward I to help choose their new king, but the man they chose recognised Edward I as his overlord and he was soon in conflict with the rest of the Scottish nobility. The Scots nobles refused to provide Edward with military support, and sealed an alliance with France which was the beginning of ‘The Auld Alliance’. William Wallace (celebrated in the film Braveheart) then led the Scots into a long conflict with England.
Robert the Bruce
Wallace was captured and executed in 1305. The Scottish throne was seized by Robert the Bruce who was crowned at Scone in 1306. Bruce eventually defeated an English army at Bannockburn 1314 and Scotland regained its independence from the English crown. It remained separate from and usually at cross purposes with England for the next three centuries.
England and Scotland unified
The two countries came together under one ruler, James VI of Scotland and I of England, in 1603 and were unified with one parliament in the reign of Queen Anne in 1707. How different would things have been if the two kingdoms had been brought together by a marriage between those two children at the end of the thirteenth century?