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).