Ostfriesland (literally "Eastern Frisia") is a coastal region in the northwest of the German federal state of Lower Saxony. It connects Western Frisia (in the Netherlands) with the districts of Dithmarschen and Nordfriesland ("Northern Frisia") in Schleswig-Holstein.
Ostfriesland consists of the districts of Aurich, Leer, Wittmund and Friesland, as well as of the cities of Emden and Wilhelmshaven. (The district of Friesland is culturally and historically distinct, but belongs nonetheless to the geographical region called Ostfriesland.)
There is a chain of islands in front of the coast, called the East Frisian Islands (Ostfriesische Inseln). These islands are (from west to east) Borkum, Juist, Norderney, Baltrum, Langeoog, Spiekeroog and Wangerooge.
Until the late Middle Ages Ostfriesland was a land populated by clans and ruled by chieftains, who resisted the attempts of German states to conquer the coasts. The first proven historical event was the arrival of a Roman fleet under Drusus in 12 BC; the ships sailed into the course of the Ems river and returned.
The Frisians appear to have arrived in the region about 500, but Ostfriesland was settled much earlier by other peoples. Frisia was a short-lived kingdom, that was crushed by Pippin of Herstal in 689. Ostfriesland became a part of the Frankish Empire, but later fell back to a land of clans. The Frisians controlled the mouth of the Ems river and threatened the ships coming down the river. For this reason the state of Oldenburg made several attempts to subjugate Ostfriesland during the 12th century. Thanks to the swampy terrain the Frisian peasants defeated the Oldenburgian armies every time. In 1156 even Henry the Lion failed to conquer the region.
The conflicts lasted for the next centuries. In the 14th century Oldenburg had given up all plans to conquer Ostfriesland. They restricted to irregular invasions, killed the livestock and returned. In the meantime the Frisians became a threat to the ships of the powerful Hanseatic League, since they attacked their ships as pirates. In 1400 a punitive expedition of the Hanseatic League against Ostfriesland succeeded. The chieftains had to promise to discontinue their support for the pirates. In 1402 the most famous pirate, Klaus Störtebeker (who was not a Frisian by birth), was captured and executed in Hamburg.
In the following years the chieftains were tamed. After 1465 they called themselves counts and no longer chieftains, and they accepted the sovereignty of the Holy Roman Empire. However, in 1514 the emperor ordered, that a duke of Saxony should be the heir to the count of Ostfriesland. Count Edzard of Ostfriesland resisted to accept this order and was outlawed. 24 German dukes and princes invaded Frisia with their armies. Despite their numerical superiority they failed to defeat Edzard, and in 1517 the emperor had to accept Edzard and his descendants as counts of Ostfriesland.
In 1654 the counts were elevated to the rank of princes. The East Frisian independency ended in 1744, when Prussia annexed the region. There was no resistance to this takeover, since it was arranged by contract before. After the Napoleonic Wars Prussia had to cede Ostfriesland to the kingdom of Hanover.