The Hanseatic League

The Works in Progress magazine has an interesting piece on the rise and fall of the Hanseatic League:

The original hansas were bands of Germanic merchants who traveled together for protection against pirates at sea, robber bandits on the riverways, and bandits and brigands on land. Each hansa originated from a common region. There were hansas from Cologne, Hamburg, Lubeck, Dortmund, and scores of other towns. 
The Hanseatic system would ultimately organize around four major trading outposts, known as kontors: London in England, Bruges in Flanders, Novgorod in Russia, and Bergen in Norway. Each of these kontors has its own history, but the most significant lessons in Hanseatic coalitions can be drawn from London.
Politically, the Hansa was a coalition. But economically it was a cartel. It did not just fight obstacles to trade but, specifically, obstacles to their trade. Those obstacles could include competing merchant communities, which they addressed with the most thinly veiled threats. Consider this message dispatched from the Prussian Hansa towns to Nurnberg merchants in 1399:
Dear friends. We wish to inform your worships that some of your fellow burgesses have this year sent copper and other goods by sea to Flanders, which has never happened before and has no precedent. Therefore, dear friends, we warn you and yours in all friendship and beg you to ban and forbid this practice in the future, as we fear – if this practice should continue – that you and yours would thereby suffer loss, for which we would be very sorry . . . 
The Hanseatic cartel was mighty and menacing when it was united. But as it found out, cartels are notoriously difficult to keep together. The cartel had to navigate defection at every layer. At first, the challenge was maintaining unity between different regional communities. But even after the kontors established themselves, they had to deal with individual merchants defecting from boycotts. And then, when the Hanseatic League formed, it had to deal with the issue of local Hansa merchants ‘leaking’ their trading privileges to their non-Hansa partners.