How a medieval trade tax sparked a war that reshaped Northern European power
When King Eric of the Kalmar Union imposed tolls on ships passing through the Oresund, he triggered a brutal conflict with the powerful Hanseatic League. This trade war, lasting from 1426 to 1435, pitted Scandinavian kingdoms against German merchant cities, ultimately altering the balance of power in the Baltic region.
The conflict originated from King Eric of Pomerania’s desire to assert independence from the Hanseatic League’s long-standing trade monopoly. By opening Baltic routes to Dutch merchants and introducing the Sound Dues—a tax on all foreign vessels traversing the Oresund—Eric directly challenged the privileges granted to the League under the Treaty of Stralsund. In response, six major Hanseatic cities, led by Lübeck, declared war in 1426, initiating a naval blockade that severely disrupted Scandinavian commerce.
The war was far from a unified effort. While the Wendish, Pomeranian, and Saxon cities spearheaded the aggression, many other Hanseatic members, including Prussian and Livonian towns, refused to participate due to the economic damage caused by the blockade. The fighting saw shifting fortunes, including a notable Danish naval victory in the Oresund and the capture of a Hanseatic salt fleet. However, internal instability plagued both sides; Wismar experienced a bloody revolt, and Eric faced the Engelbrekt Rebellion in Sweden, which forced him to manage multiple fronts simultaneously.
By 1435, the strain of these concurrent conflicts forced Eric to sign the Peace of Vordingborg. The terms were a significant defeat for the Kalmar Union: the Hanseatic League secured exemptions from the Sound Dues, gained control of the fort of Helsingborg, and forced the cession of Schleswig to the count of Holstein. These concessions weakened Eric’s authority, leading to his eventual deposition. Although the Kalmar Union later attempted to revive its influence by favoring Dutch traders, the animosity between Denmark and the Hanseatic League persisted for centuries, defining the geopolitical landscape of the Baltic until the 17th century.
Source: Dano-Hanseatic War (1426–1435)
