In the ruling dynasties and noble families of much of Europe and Asia, the family's major assets (realm, titles, fiefs, property and income) have historically been passed from a father to his firstborn son in what is known as primogeniture; younger sons, the cadets, inherited less wealth and authority (such as a small appanage) to pass on to future generations of descendants.
In such cases, primary responsibility for promoting the family's prestige, aggrandizement, and fortune fell upon the senior branch for future generations.
Some cadet branches came to inherit the crown of the senior line, e.g. the Bourbon Counts of Vendôme mounted the throne of France (after civil war) in 1593; the House of Savoy-Carignan succeeded to the kingdoms of Sardinia (1831) and Italy (1861); the Counts Palatine of Zweibrücken obtained the Palatine Electorate of the Rhine (1799) and the Kingdom of Bavaria (1806); and a deposed Duke of Nassau was restored to sovereignty in the Grand Duchy of Luxembourg (1890).
A still more junior branch of the Wettins, headed by the rulers of the small Duchy of Saxe-Coburg and Gotha, would, through diplomacy or marriage in the 19th and 20th centuries, obtain or consort and sire the royal crowns of, successively, Belgium, Portugal, Bulgaria and the Commonwealth realms.
Also, marriage to cadet males of the Houses of Oldenburg (Holstein-Gottorp), Polignac, and Bourbon-Parma brought those dynasties patrilineally to the thrones of Russia, Monaco, and Luxembourg, respectively.