Disunited Kingdoms

In the last decades of the thirteenth century the British Isles appeared to be on the point of unified rule, dominated by the lordship, law and language of the English. However by 1400 Britain and Ireland were divided between the warring kings of England and Scotland, and peoples still starkly defined by race and nation. Why did the apparent trends towards a single royal ruler, a single elite and a common Anglicised world stop so abruptly after 1300? And what did the resulting pattern of distinc