The League was an association of Northern German Cities and Towns. Formed around 1250, The League dominated trade and commerce for hundreds of years. During it's heyday, The League boasted some 200 Towns. As the Cities of The League were dominated by the Merchant Class, the majority of League work was in the areas of mutual protection (with regards to commerce and trading). The League created a monopoly in grain, amber, timber and furs during their tenure. As time progressed, the need to create a practical military defense arm developed.
This was due to the increased Piracy along their principle sea routes. Joining The League imparted serious financial and prestige to it's members. Developing better shipping (with regards to ship building), increased profits (especially with well armed fighting vessels). This meant more of the imports and exports reached member countries (and their buyers). Although disputed by the only viable political power in their sphere of influence – The Holy Roman Empire – they could do nothing to really effect them.
The League's naval superiority grew so strong that all they had to do was to embargo their enemies. The decline of The Hanseatic League developed around the 14th Century. The rise of The “Black Death” hurt commerce and dangers for shipping greatly increased. Outside Merchants began to undermine The League's power. Surviving until 1699 (with only 9 member Countries), they disbanded (as the Medieval association of Communes could not endure into the emerging world of National Monarchies).