[1] The heir of a junior line of the Greek branch, through Prince Philip, Duke of Edinburgh, hold the thrones of the United Kingdom and the other Commonwealth realms after the passing of Queen Elizabeth II.

Elimar's descendants appear as vassals, though sometimes rebellious ones, of the dukes of Saxony; but they attained the dignity of princes of the empire when the emperor Frederick I dismembered the Saxon duchy in 1180.

[1] During the early part of the 13th century, the counts carried on a series of wars with independent, or semi-independent, Frisian princes to the north and west of the county, which resulted in a gradual expansion of the Oldenburgian territory.

In 1460, he inherited the Duchy of Schleswig and the County of Holstein, an event of high importance for the future history of Oldenburg.

Lutheranism was introduced into the county by Anthony I (1505–73, r. from 1529), who also suppressed the monasteries; however, he remained loyal to Charles V, Holy Roman Emperor during the Schmalkaldic War, and was able thus to increase his territories, obtaining Delmenhorst in 1547.

By his neutrality during the Thirty Years' War and by donating valuable horses to the warlord, the Count of Tilly, Anthony Günther secured for his dominions an immunity from the terrible devastation to which nearly all the other states of Germany were exposed.

He also obtained from the emperor the right to levy tolls on vessels passing along the Weser, a lucrative grant which soon formed a material addition to his resources.

Its annexation into the French Empire, in 1810, was one of the causes for the diplomatic rift between former allies France and Russia, a dispute that would lead to war in 1812 and eventually to Napoleon's downfall.

In 1937 (with the Greater Hamburg Act), it lost the exclave districts of Eutin near the Baltic coast and Birkenfeld in southwestern Germany to Prussia and gained the City of Wilhelmshaven.

By the beginning of World War II in 1939, as a result of these territorial changes, Oldenburg had an area of 5,375 square kilometres (2,075 sq mi) and 580,000 inhabitants.