For most of its 1,200 year history, Bremen was an independent city within the confederal jurisdiction of the Holy Roman Empire. In the late Middle Ages, its governing merchant guilds were at the centre of the Hanseatic League, which sought to monopolise the North Sea and Baltic trade. To establish and confirm its independence, the city had to contend first with the Prince-Archbishop of Bremen, and then with the Swedes, who had become the masters of the surrounding, former episcopal, duchies after the Thirty Years' War.

In the late nineteenth century Bremen was drawn by Prussia into the German Empire. Thanks to new sea wharves and anchorage at Bremerhaven, the city became Germany's main port of emigration to the Americas, and an entrepôt for her late developing colonial trade. The Norddeutscher Lloyd (NDL) was founded in Bremen in 1857 and it later became one of the world's leading shipping companies.

In the twentieth century, Bremen, a broadly liberal and social-democratic city, lost its autonomy under the Hitler regime. After the devastations of World War Two, in which two thirds of the city's fabric were severely damaged, this autonomy was restored. Bremen became one of the founding Länder (or states) of the German Federal Republic. From the late 1950s, the post-war Wirtschaftswunder drew workers to the city from Turkey and Southern Europe, so that, combined with refugees resettled in the 21st century, around a third of Bremen's current population is of recent non-German origin.

Early history The marshes and moraines near Bremen have been settled since about 12,000 BC. Burial places and settlements in Bremen-Mahndorf and Bremen-Osterholz date back to the 7th century AD. Since the Renaissance, chroniclers have assumed that Fabiranum or Phabiranon on Ptolemy's Fourth Map of Europe (dating from AD 150) refers to Bremen. However, Ptolemy's coordinates actually suggest a site northeast of the mouth of the river Visurgis (Weser). In Ptolemy's time the Chauci lived in the area now called North-Western Germany or Lower Saxony. By the end of the 3rd century they had merged with the Saxons.

During the Saxon Wars (772–804), Widukind led a prolonged resistance to the western advance of the Franks. The Frankish king Charlemagne ultimately prevailed: thousands of Saxon nobles were massacred, and conversion to Christianity was ordered by decree. In 787 Willehad of Bremen became the first Bishop of Bremen. In 888, at the behest of Archbishop Rimbert, Kaiser Arnulf of Carinthia, the Carolingian King of East Francia, granted Bremen the rights (confirmed in 965) to hold its own markets, mint its own coins and devise its own customs laws.

The city's first stone walls were built in 1032, and the stone cathedral of St Peter's followed in 1042. These were marks of the wealth that was beginning to accumulate thanks to the North Sea trade. In the following century, Dutch settlers began to drain the surrounding wetlands and build the dikes that still characterise Bremen's surroundings.

In 1186 the Prince-Archbishop Hartwig of Uthlede and his bailiff in Bremen confirmed the Gelnhausen Privilege, by which Frederick I Barbarossa granted the city considerable legislative and fiscal autonomy. Property within the municipal boundaries was freed from feudal taxes, including serfs, who were considered free if they had lived in the city for at least one year and a day. The foundation for Bremen's later claim to its status as a Free Imperial CitySiehe Thomas Hill: Die Stadt und ihr Markt. VSWG – Vierteljahrschrift für Sozial- und Wirtschaftsgeschichte / Beihefte Nr. 172, Franz Steiner Verlag, Bremen 2004, , S. 235 lay in this imperial privilege, which was confirmed and expanded by Archbishop Gerhard II in 1233, in return for assistance in the Stedinger Crusade.

The city's remaining tax obligations to the Prince-Archbishop were both a burden and a lever of influence. The city participated in the Diet or Landtag of the Archbishopric of Bremen, where as the main taxpayer it could obtain further concessions.

Hanseatic League In 1260 Bremen joined the Hanseatic League. A trade cartel of northern European towns, the league was centred in Lübeck, a base for merchants from Saxony and Westphalia trading in the eastern Baltic. This was a source of timber, wax, amber, resins, and furs, along with rye and wheat brought down on barges from the hinterland to port markets. Of equal importance to the powerful merchant guilds, or Hansa, of Bremen was the League's ability to control the North Sea salt-fish trade, and above all the Scania Market.

Bremen was engaged in numerous military actions taken by the League, all aimed at maintaining and enhancing collective privileges. In the 1440s the city also engaged privateers on its own initiative, in order to attack the League's rivals in the North Sea. One notorious captain, known as Grote Gherd ("Great Gerry"), managed to capture thirteen ships from Flanders in a single expedition.

Trade secured by the League brought both commerce and industry to Bremen and its surrounding region. Newer and finer woollen and linen fabrics, and even silks, were manufactured locally. The artisanal refinement of products from the textile industry could be found in other fields as well, such as etching, wood carving, armour production, engraving of metals, and wood-turning. Trade also increased exchanges with Italy and the Mediterranean, ensuring the early arrival of the Renaissance in northern Germany. A legacy from that period is the regional architectural style known as the Weser Renaissance, which characterises the embellished facade added to the Bremen Rathaus in 1612.

As for the League in general, much of the drive for the co-operation between otherwise rival cities derived from the fragmented nature of existing territorial governments, which had failed to provide security for trade. However, the League's importance declined in Bremen in the 16th century, as the United Dutch Provinces entered the competition and as greater princely authority consolidated, creating powerful monarchies such as Sweden, Denmark-Norway, Brandenburg-Prussia and England. The last of the League's great trading posts (or Kontors), in Bergen, closed in 1754.

Struggle with the Prince-Archbishop

In 1350 Bremen was a city of 20,000, its trade flourishing thanks to the Hansekogge (cog ship), a unique product of its shipbuilders. Despite this, conflict with the Prince-Archbishop and other magnates in the surrounding country continued. In 1365, new taxes were levied to ransom burghers held hostage by Gerhard III, Count of Hoya, triggering a popular uprising in the city that was only put down by the city council after much bloodshed.

In response to the Prince Archbishop's attempts to exploit its internal struggles, the city further enhanced its fortifications. A particularly narrow gate, the so-called Bishop's Needle (, first mentioned in 1274), was built and reserved for all clergymen, including the Prince-Archbishop himself. The narrowness of the gate was intentional, as it made it physically impossible for the bishop to enter the city surrounded by his knights. Despite these measures, factionalism permitted Prince-Archbishop Albert II of Brunswick-Wolfenbüttel to seize the city on the night of 29 May 1366. Still, within a month several exiles, with the assistance of the Count of Oldenburg, managed to recover the city and executed the collaborators.

By the end of the 1360s, Albert's growing indebtedness placed Bremen in a favourable position, as the city was able to effectively purchase not only his rights in the city, but also his many surrounding fortresses and bailiwicks.

In 1381 the city's troops successfully ended the brigandage by other impecunious landed magnates and knights by itself becoming their liege lord, and thereby extending its control along the lower course of the Weser. As a measure of its new power and independence, in 1404 the city replaced its old wooden statue of Roland with a larger limestone model, which still stands today before the Rathaus in the central market place.

In 1421 Bremen reached its greatest extent, when the Duchy of Saxe-Lauenburg and the stricken Knights of Bederkesa pawned their lands on both sides of the lower Weser.Otto Edert, Neuenwalde: Reformen im ländlichen Raum, Norderstedt: Books on Demand, 2010. .

Reformation

Bremen, long hostile to its Prince-Archbishop and the temporal power and pretensions of the Church, readily embraced the Protestant Reformation, as it swept across Northern Germany in the late 1520s. In 1532, Bremen's burghers forcefully interrupted Catholic Mass in St Peter's cathedral, the Bremer Dom, and prompted a pastor to hold a Lutheran service in its place. The Prince-Archbishop, who still retained sovereign control of the cathedral (one of his last rights within the city), shut its doors. Despite this, he was unable to stem the tide of conversion to the Reformed faith/Calvinism, even within the communities under his direct authority.

In 1547, the prevailingly Lutheran cathedral chapter appointed the Dutch Albert Hardenberg, called Rizaeus, as the cathedral's first Protestant pastor. Rizaeus, however, turned out to be of Zwinglian persuasion, which, after heated disputes, led to the cathedral closing its doors again in 1561, only to fully reopen them in 1638.

By the 1590s the majority of Bremen's burghers and city council had adopted Calvinism, in contrast with the cathedral chapter, which had remained Lutheran under the administration of the Prince-Archbishopric.Friedrich Seven (1997,: Niederländische Einflüsse auf die 1. und 2. Reformation in Bremen. In: Bremen und die Niederlande. Jahrbuch 1995/96 der Wittheit zu Bremen, Bremen. This antagonism between a Calvinistic majority and the Lutheran minority that was to retain control of the cathedral until 1803 (when finally it was mediatised as part of the city), continued well into the 19th century. The conflict was conclusively resolved only in 1873, when the Calvinist and Lutheran congregations of Bremen reconciled under the administrative umbrella of the Bremen Protestant Church.

Thirty Years' War Soon after the beginning of the Thirty Years' War Bremen declared its neutrality. In 1623 it rejected the appeal of the Republic of the Seven United Netherlands to assist it in its struggle for independence against Habsburg Spain and imperial forces. Nonetheless, Imperial troops under Albrecht von Wallenstein and those of the Catholic League headed north. Wallenstein had visions of breaking-up the Hanseatic League, and of establishing new Baltic trade monopolies to benefit imperial favourites. In 1628, Bremen paid Wallenstein a hefty ransom to spare itself a siege, and by such means it was able to avoid occupation throughout the war.

In 1629 an imperial Edict of Restitution ordered Bremen to restore properties and rights within the city, including control of the cathedral, to a once again Catholic Prince-Archbishop. The city refused, stating it would rather separate from the Holy Roman Empire and join the Dutch in their Republic.Dutch independence was finally confirmed by the Treaty of Westphalia in 1648. The intervention of the Lutheran Swedes under Gustavus Adolphus saved the city from an imperial siege. However, once Swedish forces had gained control of the former episcopal territories around the city (an occupation that was confirmed by the Treaty Westphalia in 1648), Bremen sensed a new threat to its independence.

Bremen had appealed for an imperial confirmation of its imperial immediacy, which, it argued, had been implicit in the Gelnhausen Privilege of 1186. In 1646 Ferdinand III, Holy Roman Emperor, granted the request in the Diploma of Linz, recognising Bremen as a Free Imperial City.

Swedish wars