While I was looking for information about some northern German states, a word came up in most of the texts I was reading through, Hanseatic. This word refers to the Hanseatic League. 

It was a merchant association between some cities on northern Germany and Baltic area headed by Lübeck. Business scenario in the Middle Ages was dangerous and risky, then merchants used to travel together to protect themselves. The Hanseatic League dominated the economy in Europe and influenced many cities. Belonging to Hansa was worthy, because they protected each other and they have priority on selling and buying products.

 Source: by Valter Pitta

The northern states had some associations, but the association between Hamburg and Lübeck inspired many others cities to become part of this association. The cities that belongs to the Hansa had autonomy, these cities were independent but they had to contribute with military and financial support to Hansa.  However, this system was dissolved with the treaty of Westphalia in 1648. Although, the Hanseatic League is so great and important that in present time Hamburg and Bremen refers themselves as a Hanseatic cities.