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.
George III of the United Kingdom George III (George William Frederick; 4 June 1738[c] – 29 January 1820) was King of Great Britain and Ireland from 25 October 1760 until the union of the two countries on 1 January 1801, after which he was King of the United Kingdom of Great Britain and Ireland until his death in 1820. He was concurrently Duke and prince-elector of Brunswick-Lüneburg ("Hanover") in the Holy Roman Empire before becoming King of Hanover on 12 October 1814. He was the third British monarch of the House of Hanover, but unlike his two predecessors, he was born in Great Britain, spoke English as his first language,[1] and never visited Hanover.[2]