The Kingdom of Hanover started out as a promising new era for the people of the region. After being for over a century in a personal union with Great Britain, the Hanoverians now were able to become an independent nation. 

Unfortunately for them, that period only lasted for less than 30 years before it was absorbed into Prussia.

This happened out of a personal hatred for the Prussians by its King Georg V. A blind person who was though related to the Hohenzollerns, he fewred the Prussian influence in his kingdom. To counter this, he made an alliance with the Austrian Empire for the war that was to come.

But he was unable to see (pun intended) that this would be a terrible move for Hanover. Prussia won the war and led to the kingdom being anexed by Berlin. For Prussia, this anexation resulted in mergins the Brandeburg territories with those in the Rhineland. But for the House of Welf, the dynasty that ruled the region for centuries, it meant a life in exile.

The family fled for Austria and a rivalry with the Hohenzollerns formed. This would only end in 1913 when Georg's grandson, Ernst August, married Viktoria Louise, the daughter of Kaiser Wilhelm ii. This marriage not only reconciled the families, but it allowed Ernst August to inherit the Duchy of Brunswick.

Now the Duchy had been ruled for centuries by a distant branch of the Welfs, but when that died out, Ernst's family became the inheritors of it. And so, the Hanoverian Family returned as german royals once more. But only briefly as 5 years and a world war later, the monarchies of Germany ended and Germany became a republic.

But the legacy of Hanover still persisted and when Germany was rebuilding after ww2, the region of Lower Saxony was made mostly out of the former territories of the Kingdom of Hanover and the Duchy of Brunswick.

Kingdom of Hanover: fell too early