Because Britain was originally four countries, in the Middle Ages, Scotland was Scotland and England was England, and the gap was as big as Germany and France. But England invaded the Principality of Wales from the Plantagenet Dynasty, and finally completely mastered the Principality of Wales. James VI, King of the Stuart Dynasty in Scotland, succeeded to the throne of England and became James I by virtue of his maternal lineage, thus forming a confederation between England and Scotland. But there are two sets of governments to govern the two, and the only thing in common is that the king is the same person. Just as the Manchu emperor inherited the title of Emperor China and the title of Mongolian Khan at the same time (and the Austro-Hungarian Empire, the Austrian emperor will also serve as the king of Hungary. On the other hand, Ireland was invaded by Britain. After the British bourgeois revolution, it was merged into Britain. At first, the full name of Britain was "United Kingdom of Great Britain and Ireland". Later, although Ireland became independent, the north was always controlled by the British, so the full name of Britain was changed to today's "United Kingdom of Great Britain and Northern Ireland".