The American data website FiveThirtyEight is following the 7 May election in the United Kingdom. They’ve kicked off their coverage with a helpful Brief Political History of the United Kingdom, which does a bloody good job of explaining what the UK is and how it got that way. The guts is:
Wales was integrated into the Kingdom of England in 1535 under Henry VIII but had been ruled by England almost continuously since 1282. Six years and three wives later, Henry was proclaimed King of Ireland, which had also been controlled to varying degrees by England since the 1100s. When Queen Elizabeth I died in 1603, the next in line to the thrones of England and Ireland was King James VI of Scotland, who then became King James I of England.
For the next hundred years, the same person reigned over England (including Wales), Scotland and Ireland, but they remained three separate kingdoms with separate governments and separate parliaments. In 1707, the Acts of Union joined England and Scotland into the “Kingdom of Great Britain,” and in 1801, Ireland joined the “United Kingdom of Great Britain and Ireland.”
Plus they have recent voting data that shows the transformation of its politics from a two-party dominated system to one where 14 parties have a reasonable shot at being represented in Westminster.