The Hanseatic League was a confederation of towns around the Baltic Sea.
Also, it wasn't strictly a German phenomenon, Scandinavian and Latvian and Russian towns were part of it too, and the Hanseatic League towns were very much independent and out of the control of the Holy Roman Emperor.
Well, it was bigger than that ... looking it up, I found even France, Scotland & Iceland in the west.
Cities of the Hanseatic League federation:
Belarus
Polozk, Vitebsk
Belgium
Bruges
England
Boston, Ipswich, King's Lynn, Kingston upon Hull
Estonia
Narva, Pärnu, Tallinn, Tartu, Viljandi
Finland
Turku, Ulvila
France
La Rochelle
Germany
Ahlen, Alfeld, Anklam, Attendorn, Bad Iburg, Balve, Beckum, Bockenem, Brakel, Brandenburg, Braunschweig, Breckerfeld, Bremen, Brilon, Buxtehude, Demmin, Dorsten, Dortmund, Drolshagen, Duderstadt, Duisburg, Einbeck, Emmerich am Rhein, Frankfurt (Oder), Fürstenau, Gardelegen, Goslar, Göttingen, Greifswald, Gronau (Leine), Halle, Haltern am See, Hamburg, Hameln, Hamm, Haselünne, Hattingen, Havelberg, Helmstedt, Herford, Hildesheim, Höxter, Kalkar/Grieth, Kamen, Kiel, Köln, Korbach, Kyritz, Lemgo, Lippstadt, Lübeck, Lüneburg, Lünen, Magdeburg, Marienmünster, Marsberg, Medebach, Melle, Meppen, Merseburg, Minden, Mühlhausen, Münster, Naumburg (Saale), Neuenrade, Neuss, Nieheim, Osnabrück, Osterburg, Osterode, Paderborn, Perleberg, Pritzwalk, Quakenbrück, Quedlinburg, Rheda Wiedenbrück, Rheine, Rostock, Rüthen, Salzwedel, Schwerte, Seehausen, Soest, Solingen, Stade, Stendal, Stralsund, Sundern, Tangermünde, Telgte, Uelzen, Unna, Uslar, Vreden, Warburg, Warendorf, Werben, Werl, Werne, Wesel, Wipperfürth, Wismar
Iceland
Hafnarfjörður, Stykkishólmur
Latvia
Cesis, Koknese, Kuldiga, Limbaži, Riga, Straupe, Valmiera, Ventspils
Lithuania
Kaunas
Netherlands
Bolsward, Deventer, Doesburg, Elburg, Groningen, Harderwijk, Hasselt, Hattem, Kampen, Maasbommel, Oldenzaal, Ommen, Rijssen, Roermond, Stavoren, Tiel, Venlo, Zutphen, Zwolle
Norway
Bergen
Poland
Bialogard, Braniewo, Chelmno, Darlowo, Elblag, Frombork, Gdañsk, Goleniów, Kolberg, Koszalin, Krakow, Kwidzyn, Lebork, Malbork, Olsztyn, Slawno, Slubice, Slupsk, Stargard, Strzelce Opolskie, Szczecin, Torun, Wroclaw
Russia
Belozersk, Ivangorod, Kaliningrad, Kingisepp, Porkhow, Pskow, Smolensk, Tikhvin, Torzhok, Totma, Twer, Velikij Ustjug, Veliky Novgorod, Vyschnij Volotschjok, Wologda
Scotland
Aberdeen, Edinburgh
Sweden
Kalmar, Nyköping, Skanör-Falsterbo, Visby