 The Global Parliament of Mayors is a...
From the middle of the 13th century, and for some 300 years after, many settlements dotted along this route formed the prosperous Hanseatic League, a European trading confederation of market towns, before the rise of the nation state led to its dissolution. The League is most easily understood as a loose federation of cities that acted together in self-interest to promote trade. "So it is not unrealistic to think of cities as discrete entities that compete and collaborate with each other, independently from the states to which they belong." In some ways it was an exercise in what we today call 'soft diplomacy'.
 ...a kind of Hanse of all cities.
 ...common platform for action.  ...a monitor of culture and economic status.  ...a kind of Hanse of all cities.  ...a governing body like the UN.