What it says on the tin, what's the earliest Scotland could become part of England? By "bering part of England" I mean either through outright conquest, English royal family rulling Scotland and be recognised as monarchs of Scotland, through marriage or kingdoms forming new entity which has to be dominated by English with capital in England (can be something different than London, if you wish) so OTL Union of Crowns of 1603 doesn't count (since they were still separate kingdoms) but Acts of Union of 1707 does (since it became united kingdom)