Hey Guys,
Random thought, but how could you make all the 'best bits' of Scotland (i.e. The lowlands) have a predominantly English population and thus be an official part of England (annexed by England), while the bits left over (the Highlands) are still very Scottish before a political unification (if there would be one in such a timeline).
This is actually very easy. Simply have the petty kingdoms of the Lowlands fall into the English orbit rather than the Scottish. For example in the west the forces of Strathclyde (alongside those of Alba, which became Scotland) were defeated by the English at the Battle of Brunanburh in 937, and Strathclyde only passed under Scottish control sometime in the 11th century. Lothian, to the West only fell under Scottish control in 1018, and William the Conqueror invaded it up until the Forth, but elected not to keep it. Galloway, in the south-west was pretty much independent through the 12th and 13th centuries.
I was thinking something along the lines of England winning wars against the Scots then either moving them [the Scots] overseas in large amounts, or through mass immigration of English settlers or something.
As I say, not required. Consider this linguistic map:
As time passed, the use of Gaelic retreated northwards and English expanded west.
How could you do this? The POD has to be after 1250 at least.
That makes it slightly more challenging, but not much, as it post-dates the 1237 Treaty of York which agreed what is virtually the Scottish border. After then, the English kings became more interested in asserting overlordship over all of Scotland rather than nibbling pieces off. What we probably need to do here is have a PoD that weakens Scotland so that they fair more poorly later on.
So, I propose the PoD that Haakon IV of Norway's fleet doesn't get wrecked by a storm in 1263, and the ATL equivalent to to the Battle of Largs is a resounding victory, resulting in the death of Alexander III, and the early collapse of Scotland into the chaos of an interregnum. His heir apparent at this point is his three year old daughter Margaret, although this will change shortly afterwards with the birth of his son, Alexander IV.
Now, I imagine that under normal circumstances, Henry II of England would step in here, as he is the father of the now widowed Queen of Scotland, but he's currently in dispute with his barons, and is unable to act.
So, it's quite plausible that, essentially, Scotland disintegrates. It's only really been in its current form for 250 years, and their are still strong peripheral forces. If the lords of Galloway, Strathclyde, Dunbar etc can't agree on who's going to be Regent, then Margaret and Alexander could easily become casualties of the chaos.
This of course could have a whole set of intriguing impacts on de Montfort's "democratic" rebellion in England, but I won't go into these in too much detail - for example, the accident which prevented him attending the arbitration at the Amiens would almost certainly be butterflied. A surviving British parliament - including elected commoners would be a very interesting divergence here.
So, assuming that the civil war in England ends on schedule in 1267, it's quite possible that there is no direct heirs for Henry to intervene in support of left in Scotland. I can easily see the English, particularly the future Edward I, playing a long game here and giving support to the southern Scottish lords in return for direct fealty. Eventually, say by 1300, Scotland will reunify, but Lothian, Strathclyde and Galloway could easily be considered as English by this point