The senior Swabian branch is less well known to history than the junior Franconian line, the latter of which became Burgraves of Nuremberg and later ruled Brandenburg and Prussia, and the German Empire.

When the last count of Hohenzollern, Karl I (1512–1579) died, the territory was divided among his three sons: The princes of Hohenzollern-Sigmaringen ruled over a small principality in south-western Germany, with a seat at Sigmaringen Castle.

The principality became a sovereign state in 1815 after the abolition of the Holy Roman Empire in 1806 and an independent realm following the Napoleonic Wars in 1815.

Prussian troops arrived in August 1849, and in a treaty signed in December Hohenzollern-Sigmaringen was annexed by Prussia, effective in March 1850.

French opposition to the candidacy of Carol's elder brother Prince Leopold for the throne of Spain triggered the Franco-Prussian War (1870–1871), which led to the founding of the German Empire in January 1871.

From 1806 until 1813 the Hohenzollern lands were a realm of the Confederation of the Rhine, a short-lived state set up by Napoleon I Bonaparte.

The English translation is: His Serene Highness (HSH) [name] by the Grace of God, Prince of Hohenzollern, Burgrave of Nuremberg, Count of Sigmaringen, Veringen and Berg, Lord of Haigerloch and Wehrstein.

The modern state of Romania was formed by union of the principalities of Moldavia and Wallachia in 1859, under the prince domnitor Alexandru Ioan Cuza.

In return for reverting to the Russian Empire three southern Bessarabian districts that had been regained by Moldavia after the Crimean War in 1852, Dobruja was acquired.

Shortly after taking the throne, Ferdinand, a Roman Catholic like his predecessor, agreed to have his children reared in the Romanian Orthodox Church.

Following cession of their sovereignty over the principality to their kinsmen the kings of Prussia in 1849, the heirs of Karl Anton continued to bear the same title, "Prince (Fürst) of Hohenzollern":