Usually, a federation is formed at two levels: the central government and the regions (states, provinces, territories), and little to nothing is said about second or third level administrative political entities. Brazil is an exception, because the 1988 Constitution included the municipalities as autonomous political entities making the federation tripartite, encompassing the Union, the States, and the municipalities. Each state is divided into municipalities (municípios) with their own legislative council (câmara de vereadores) and a mayor (prefeito), which are partly autonomous from both Federal and State Government. Each municipality has a "little constitution", called "organic law" (lei orgânica). Mexico is an intermediate case, in that municipalities are granted full-autonomy by the federal constitution and their existence as autonomous entities (municipio libre, "free municipality") is established by the federal government and cannot be revoked by the states' constitutions. Moreover, the federal constitution determines which powers and competencies belong exclusively to the municipalities and not to the constituent states. However, municipalities do not have an elected legislative assembly.

When is a federation formed?