The Treaty of York was an agreement between the kings Henry III of England and Alexander II of Scotland, signed at York on 25 September 1237, which affirmed that Northumberland (which at the time also encompassed County Durham), Cumberland, and Westmorland were subject to English sovereignty. This established the Anglo-Scottish border in a form that remains almost unchanged to modern times (the only modifications have been regarding the Debatable Lands and Berwick-upon-Tweed). The treaty detailed the future status of several feudal properties and addressed other issues between the two kings, and historically marked the end of the Kingdom of Scotland's attempts to extend its frontier southward.