There was a time when the House of Luxembourg was the main rival to the Habsburgs for control of central Europe, contributing four Holy Roman Emperors:
https://en.wikipedia.org/wiki/Duchy_of_Luxemburg
The dukes of this area used to be so important to European politics that Henry VIII of England married a Dutch duke's daughter for political reasons (and immediately regretted it of course, as he was wont to do).
The area of the Duchy used to be several times larger, but over centuries it was nibbled away by France, Prussia, and finally the creation of Belgium.
It has been under Spanish rule (those Habsburgs again), then invaded by the French revolutionary republic and annexed into France as a department simply called Forêts (Forests) because the revolutionaries didn't want to keep any names that honored the old nobility. After Napoleon's defeat the Congress of Vienna aimed to restore old borders and reinstate monarchies, but with multiple claims on Luxembourg, it was split and became a grand duchy whose head of state was the King of Netherlands.
It became an independent country in 1890 when the Dutch king died without a male heir. Dutch law allowed the throne to pass to a female child, but the Grand Duchy was under different laws and was inherited by a claimant rather than the new Dutch queen. (Monarchy is pretty weird in practice.)