Brunswick-Lüneburg (Braunschweig-Lüneburg, also Brunswick-Lunenburg) was a historical ducal state during the period from the late Middle Ages through the late Early Modern era within the North-Western domains of the Holy Roman Empire.
As the name implies, the main cities of this feudal state were Braunschweig (Brunswick) and Lüneburg through much of the late Middle Ages. Eventually Hanover, currently the capital of the federal state (or in German, Bundesland) of Lower Saxony (Niedersachsen), grew into a city that economically dominated the region and later dukes made it their main administrative seat while keeping the family seat in the historic domain, hence giving one reason of the change to the title when the family ascended to the more recent and more prestigious rank of "Elector".
The first duke of Brunswick-Lüneburg was Otto I, grandchild of Henry the Lion, who reigned from 1235 onwards. After 1267 his sons split the duchy into two parts, the Lüneburg-Celle line of John and the Wolfenbüttel line of his brother Albert, which later became a multitude of smaller states. All of them were ruled by the Welf or Guelph dynasty and maintained close relations—not infrequently by the practice of marrying cousins— a practice far more common than one might think, even among the peasantry of the Holy Roman Empire, for the salic inheritance laws in effect, encouraged the practice of retaining control of lands and benefits. The centres of power moved in the meantime from Braunschweig and Lüneburg to Celle and Wolfenbüttel.
While there is a total of about a dozen subdivisions that existed, some of them were only dynastic and were not recognised as states of the Empire, which at one time had over 1500 such legally recognized entities. In the List of Reichstag participants (1792), the following four subdivisions of Brunswick-Lüneburg had recognized representation:
By 1705, outside of the Hanovarian dynasty ruling England, only two Dukes of Brunswick-Lüneburg survived, one ruling Calenberg, Celle, and other possessions, and the other ruling Wolfenbüttel.
As a latter day development, what became the Electorate of Hanover was initially called the Elector of Brunswick-Lunenberg when the Holy Roman Emperor appointed Ernest Augustus, Duke of Brunswick-Lunenberg an Elector in 1696 (two years before his death) in a somewhat controversial move to increase the number of Protestant electors—thereby offending the entrenched interests of the extant prince-electors who would no longer be so few&mdash. As with most matters in Europe during these times, this was part of the centuries-long religious unrest accompanied by outright warfare (see Thirty Years' War) triggered by the zealous advocates on either side of the Protestant Reformation and the Catholic Counter-Reformation. Clearly, these masked dynastic ambitions of grasping noblemen.
The territories of Calenberg and Lüneburg-Celle were made an Electorate by the Emperor Leopold I in 1692 in expectation of the imminent inheritance of Celle by the Duke of Calenberg, though the actual dynastic union of the territories did not occur until 1705 under his son George I, and the Electorate was not officially approved by the Imperial Diet until 1708.
The resulting state was known under many different names (Brunswick-Lüneburg, Calenberg, Calenberg-Celle, Electorate of Hanover); its ruler was often known as the "Elector of Hanover". Coincidentally, in 1701 the Duke of Brunswick-Lüneburg found himself in the line of succession for the British crown later confirmed in 1707, by the Act of Union, and inherited that creating a personal union of the two crowns in 20 October 1714.
After a little over a decade, the matter of the disputed electorate was settled upon the heir, and the new Duke of Brunswick-Lüneburg (acceded as duke on 23 January 1698), George Louis I was able to style himself the Elector of Hanover (or as is called by some using a family-seat engendered root, the "Elector of Calenberg") from 1708. It was not just happenstance but similar religious driven politics that brought about the circumstance that he was also been put into line of succession for the British crown by the Settlement Act of 1701— which was written to ensure a Protestant succession to the thrones of Scotland and England in a day when anti-Catholic sentiment ran high in much of Northern Europe and much of Great Britain. In the event, George I succeeded his second cousin Queen Anne of Great Britain — the last reigning member of the House of Stuart, and subsequently formed a personal union from 1 August of 1714 between the British crown and the duchy of Brunswick-Lüneburg (electorate of Hanover) which would last until well after the end of the Napoleonic wars more than a century later—including even through the dissolution of the Holy Roman Empire and the rise of a new successor kingdom. In that manner, the "Electorate of Hanover" (the core duchy) was enlarged with the addition of other lands and became the kingdom of Hanover in 1814 at the peace conferences (Congress of Vienna) settling the future shape of Europe in the aftermath of the Napoleonic wars.
His posterity, George II of Great Britain and George III of Great Britain retained the position of elector until the Holy Roman Empire was abolished by its last emperor in 1806, least Napoleon install enough puppets as electors to achieve his election as the Holy Roman Emperor. As one key belligerent to the war, the British king George III, contested the validity of the dissolution of the Empire and maintained separate consular offices and staff for the Electorate of Hanover until the peace conferences at the wars end. After the fall of Napoleon, George III regained his lands plus lands from Prussia as King of Hanover, whilst giving up some other smaller scattered territories. The day of small pocket states in Europe had closed. Thereafter, consolidation of larger blocks of territory in part drove European politics, and the modern states of Germany, Italy, and Belgium emerged.
The Wolfenbüttel line retained its independence, except for the period from 1807 to 1813, when both it and Hanover were merged into the Napoleonic Kingdom of Westphalia. The Congress of Vienna of 1815 turned it into an independent country under the name Duchy of Brunswick. The Duchy of Brunswick remained independent and joined first the North German Confederation and in 1871 then the German Empire.