Historically, Brandenburg was an independent country and the core of the unified German state. It was the site of Berlin, and despite technically being only a part of the Kingdom of Prussia, was the engine that drove the rise of that state.
(Need info on pre-historical Brandenburg. Beaker people, whoever....)website with info http://www.comp-archaeology.org/TRB.htm
Brandenburg between the Elbe and Vistula rivers was invaded by Slavic tribes in the middle of the first millennium, displacing the then-current German inhabitants. Charlemagne eventually checked their advances. Henry I the Fowler, king from 918-936, established the North Mark for protection from further encroachment. The church brought bishoprics, who with their walled burgs, afforded protection for the burghers from attacking marauders. With the monks and bishops started recorded history in Brandenburg.
In 948 Emperor Otto I had established German control over the Slavic inhabitants of the area and founded the dioceses of Havelberg and Brandenburg, but when he died in 983 and Slavic largely ended German control for two centuries.
For some time up until the 11th century, the area that would become Brandenburg was inhabited by the Slavic Wends. A portion of the modern population is still of this people. In 1134, in the wake of a German crusade against the Wends, the German magnate Albert the Bear was granted the North Mark by the Holy Roman Emperor Lothar II.
Albert's control of the region was merely nominal for several decades, but he engaged in a variety of campaigns against the Wends, as well as more diplomatic efforts which saw his control become more real by the middle of the century. In 1150, he formally inherited Brandenburg from its last Wendish ruler, Pribislav. Albert, and his descendants the Ascanians, then made considerable progress in Christianizing and Germanizing the lands. As a borderland between German and Slavic cultures, the country was known as the March of Brandenburg at this time.
In 1320 the Ascanian line came to an end, and for a short time Brandenburg was under the control of the Wittelsbachs, a family later more closely associated with their rule in Bavaria. After a confused period towards the end of the 15th century, however, the Margravate was granted to the house of Hohenzollern, which would rule until the end of World War I. During this time, the Margrave of Brandenburg was also named as one of the electors of the Holy Roman Empire.
Brandenburg was one of the German states to switch to Protestantism in the wake of the Reformation, and generally did quite well in the century following, expanding its lands into the Duchy of Prussia and along the Lower Rhine in Cleves and elsewhere. The result was a sprawling, disconnected country that was in poor shape to defend itself during the Thirty Years War.
Towards the end of that devastating conflict, however, Brandenburg (and its successor states) enjoyed a string of talented rulers who gradually maneuvered their country towards the heights of power in Europe. The first of these was Frederick William I, the so-called "Great Elector", who worked tirelessly to rebuild and consolidate the nation.
When Frederick William died in 1688, he was followed by his son Frederick, third of that name in Brandenburg. However, the lands that had been acquired in Prussia were outside the formal boundaries of the Holy Roman Empire, and Frederick decided to place the emphasis of his titles on what were, in actuality, vast but less agriculturally valuable stretches of sandy ground. From then on, the Hohenzollerns styled themselves "King in Prussia", a promotion from margrave. Frederick then became known as Frederick I. In actuality, Brandenburg was still the most important portion of the kingdom -- and in fact, the state was often informally referred to as Brandenburg-Prussia -- but for the purposes of accuracy, the continuation of this history can be found at Prussia.
See the state's own website,