05 May 1991,
Nineteen municipalities created the Commonwealth of Basque Municipalities. As part of the celebration of the Day of the Basque Municipalities in Aizarnazabal, the elected representatives of the municipalities interested in serving citizenship held an assembly for the creation of the UEMA. That day they gathered party and claim.
It consists of municipalities with an Euskaldunization index greater than 70%. Currently, in many towns of UEMA the use of the Basque country is also decreasing.