The Duchy of Brunswick () was a historical German state. Its capital was the city of Brunswick (). It was established as the successor state of the Principality of Brunswick-Wolfenbüttel by the Congress of Vienna in 1815. In the course of the 19th-century history of Germany, the duchy was part of the German Confederation, the North German Confederation and from 1871 the German Empire. It was disestablished after the end of World War I, its territory incorporated into the Weimar Republic as the Free State of Brunswick. History Principality of Brunswick-Wolfenbüttel The title "Duke of Brunswick and Lüneburg" () was held, from 1235 on, by various members of the Welf (Guelph) family who ruled several small territories in northwest Germany. These holdings did not have all of the formal characteristics of a modern unitary state, being neither compact nor indivisible. When several sons of a Duke competed for power, the lands often became divided between them; when a branch of the family lost power or became extinct, the lands were reallocated among surviving members of the family; different dukes might also exchange territories. The unifying element of all these territories was that they were ruled by male-line descendants of Duke Otto I (ruled 1235–1252). After several early divisions, Brunswick-Lüneburg re-unified under Duke Magnus II (d. 1373). Following his death, his three sons jointly ruled the Duchy. After the murder of their brother Frederick I, Duke of Brunswick-Lüneburg, brothers Bernard and Henry redivided the land, Henry receiving the territory of Wolfenbüttel. Duchy of Brunswick Formal sovereignty confirmed The territory of Wolfenbüttel was recognized as a sovereign state by the Congress of Vienna in 1815. It had been a portion of the medieval Duchy of Brunswick-Lüneburg. From 1705 onward, all other portions of Brunswick-Lüneburg except Wolfenbüttel had been held by the Prince of Calenberg and Celle, i.e. the Elector of Hanover, but the Wolfenbüttel line retained its independence from Hanover. The Wolfenbüttel principality had for the period from 1807 to 1813 been held as part of the Kingdom of Westphalia. The Congress turned it into an independent country under the name Duchy of Brunswick. Charles II (1815–1830) The underage Duke Charles, the eldest son of Duke Frederick William (who had been killed in action), was put under the guardianship of George IV, the Prince Regent of the United Kingdom and Hanover. First, the young duke had a dispute over the date of