Bremerhaven (literally "Bremen's harbour", Low German: Bremerhoben) is a city at the seaport of the Free Hanseatic City of Bremen, a state of the Federal Republic of Germany. It forms an enclave in the state of Lower Saxony and is located at the mouth of the River Weser on its eastern bank, opposite the town of Nordenham. Though a relatively new city, it has a long history as a trade port and today is one of the most important German ports, playing a crucial role in Germany's trade.
The town was founded in 1827, but settlements, such as Lehe, were in the vicinity as early as the 12th century, and Geestendorf, which was "mentioned in documents of the ninth century". These tiny villages were built on small islands in the swampy estuary. In 1381, the city of Bremen established de facto rule over the lower Weser stream, including Lehe, later therefore called Bremerlehe. Early in 1653, Swedish Bremen-Verden's troops captured Bremerlehe by force.
The Emperor Ferdinand III ordered his vassal Christina of Sweden, then Duchess regnant of Bremen-Verden, to restitute Bremerlehe to Bremen. However, Swedish Bremen-Verden soon enacted the First Bremian War (March to July 1654) and in the following peace treaty (Recess of Stade; November 1654) Bremen had to cede Bremerlehe and its surroundings to Swedish Bremen-Verden. The latter developed plans to found a fortified town on the site, which only later used to become Bremerhaven, and in 1672—under the reign of Charles XI of Sweden, in personal union Duke of Bremen-Verden—colonists tried unsuccessfully to erect a castle (named Carlsburg after Charles XI) there, which was meant to protect, as well as control, shipping heading for Bremen.
Finally, in 1827, the city of Bremen under Burgomaster Johann Smidt bought the territories at the mouth of the Weser from the Kingdom of Hanover. Bremen sought this territory to retain its share of Germany's overseas trade, which was threatened by the silting up of the Weser around the old inland port of Bremen. Bremerhaven (literally in ) was founded to be a haven for Bremen's merchant marine, becoming the second harbour for Bremen, despite being downstream. Due to trade with and emigration to North America, the port and the town grew quickly. In 1848, Bremerhaven became the home port of the German Confederation's Navy under Karl Rudolf Brommy.
The Kingdom of Hanover founded a rival town next to Bremerhaven and called it Geestemünde (1845). Both towns grew and established the three economic pillars of trade, shipbuilding and fishing. Following inter-state negotiations at different times, Bremerhaven's boundary was several times extended at the expense of Hanoveran territory. In 1924, Geestemünde and the neighbouring municipality of Lehe were united to become the new city of Wesermünde, and in 1939 Bremerhaven was removed from the jurisdiction of Bremen and made a part of Wesermünde, then a part of the Prussian Province of Hanover.
Bremerhaven was one of the important harbours of emigration in Europe.
As a key base of the Kriegsmarine, most of the city was destroyed in the bombing of Bremen in World War II; however, key parts of the port were deliberately spared by the Allied forces to provide a usable harbour for supplying the Allies after the war. All of Wesermünde, including those parts, which did not previously belong to Bremerhaven, was a postwar enclave run by the United States within the British zone of northern Germany. In 1947 the city became part of the federal state Free Hanseatic City of Bremen and was consequently renamed from Wesermünde to Bremerhaven. Today, Bremerhaven is therefore part of the city-state of Bremen, being to all intents and purposes a state comprising two cities, while also a city in its own right. This is complicated somewhat by the fact the city of Bremen has owned the "overseas port" within Bremerhaven since 1927. To further complicate matters, a treaty between the two cities (as mentioned in Section 8 of Bremerhaven's municipal constitution) makes Bremerhaven responsible for the municipal administration of those parts owned directly by Bremen (known as stadtbremisch).