how and when did the dukes of brandenburg become kings of prussia
List of rulers of Brandenburg The early rulers came from several different dynasties, but from 1415 Brandenburg and its successor states were ruled by the House of Hohenzollern for over 500 years. From 1618 onward, Brandenburg was ruled in personal union with the Duchy of Prussia. The Hohenzollerns raised Prussia to a kingdom as the Kingdom of Prussia in 1701, and from then on Brandenburg was de facto treated as part of the kingdom even though it was legally still part of the Holy Roman Empire. The titles of Margrave of Brandenburg and Elector of Brandenburg were abolished along with the Holy Roman Empire in 1806, and Brandenburg was formally integrated into Prussia. Despite this, the Prussian kings still included the title "Margrave of Brandenburg" in their royal style. From 1871 to 1918 the Hohenzollerns were also German Emperors.
Zollverein Historians have analyzed three Prussian goals in the development of the Zollverein: first, as a political tool to eliminate Austrian influence in Germany; second, as a way to improve the economies; and third, to strengthen Germany against potential French aggression while reducing the economic independence of smaller states.[3] The Zollverein created a larger market for German-made farm and handicraft products and promoted commercial unification under fiscally sound economic parameters. While the Union sought to limit trade and commercial barriers between and among member states, it continued to uphold the protectionist barriers against outsiders.