quality:corruption
Zenith

The weakening of imperial power and imperial protection under the late Hohenstaufen dynasty forced the League to institutionalise a cooperating network of cities with a fluid structure, called the Städtehanse, but it never became a formal organisation and the Kaufmannshanse continued to exist. This development was delayed by the conquest of Wendish cities by Danish king Eric VI Menved or by their feudal overlords between 1306 and 1319 and the restriction of their autonomy. Assemblies of the Hanse towns met irregularly in Lübeck for a Hansetag (Hanseatic Diet) – starting either around 1300, or possibly 1356. Many towns chose not to attend nor to send representatives, and decisions were not binding on individual cities if their delegates were not included in the recesses; representatives would sometimes leave the Diet prematurely to give their towns an excuse not to ratify decisions. Only a few Hanseatic cities were free imperial cities or enjoyed comparable autonomy and liberties, but many temporarily escaped domination by local nobility.

Between 1361 and 1370, League members fought against Denmark in the Danish-Hanseatic War. Though initially unsuccessful with a Wendish offensive, towns from Prussia and the Netherlands, and eventually joined by Wendish towns, allied in the Confederation of Cologne in 1368, sacked Copenhagen and Helsingborg, and forced Valdemar IV, King of Denmark, and his son-in-law Haakon VI, King of Norway, to grant tax exemptions and influence over Øresund fortresses for 15 years in the peace treaty of Stralsund in 1370. It extended privileges in Scania to the League, including Holland and Zeeland. The treaty marked the height of Hanseatic influence; for this period the League was called a "Northern European great power ". The Confederation lasted until 1385, while the Øresund fortresses were returned to Denmark that year.

After Valdemar's heir Olav died, a succession dispute erupted over Denmark and Norway between Albert of Mecklenburg, King of Sweden and Margaret I, Queen of Denmark. This was further complicated when Swedish nobles rebelled against Albert and invited Margaret. Albert was taken prisoner in 1389, but hired privateers in 1392, the socalled Victual Brothers, who took Bornholm and Visby in his name. They and their descendants threatened maritime trade between 1392 and the 1430s. Under the 1395 release agreement for Albert, Stockholm was ruled from 1395 to 1398 by a consortium of 7 Hanseatic cities, and enjoyed full Hanseatic trading privileges. It went to Margaret in 1398.

The Victual Brothers controlled Gotland in 1398. It was conquered by the Teutonic Order with support from the Prussian towns and its privileges were restored. The grandmaster of the Teutonic Order was often seen as head of the Hanse (caput Hansae), both abroad and by some League members.