3/ Scotland and England
united in 1707.
The relationship between the "constituent countries" of the UK has evolved over time.
Fans of obscure political/geographic crossover references may recall the "West Lothian question" https://en.wikipedia.org/wiki/West_Lothian_question
in 1999 Scottish Parliament was (re)established. The popular Scottish National Party advocates for independence from the UK, and this culminated in the 2014 independence referendum, with "No" winning 55.3% to 44.7%
https://en.wikipedia.org/wiki/2014_Scottish_independence_referendum