The senior Welf principality in the Harz foreland — the branch of Brunswick-Lüneburg that did NOT become Hanover. Repeatedly split and reunited, it hired its soldiers to Britain in the American war, was erased by Napoleon into the Kingdom of Westphalia in 1806, and returned at the Congress of Vienna as the Duchy of Brunswick.
Abolished in the German revolution of November 1918; its territory became the Free State of Brunswick within the Weimar Republic.
The standard older narrative history devoted to this duchy alone (reprint edition verified on Open Library).
Places the Welf partitions and the Wolfenbüttel/Lüneburg split in imperial context.