The samba school system seems to be unique to Brazil. Unlike parades such as the Rose Parade in California, for instance, the samba schools’ organizations consist almost entirely of community volunteer work. More than just musical groups, the schools are the neighborhood associations that cover a variety of community needs, such as educational resources and medical care. There are often political and commercial interests involved as well, even from abroad, especially when the samba school honors the literature, music and dance, or a myth, historic figure or event from another country. Drug lords who control trafficking in the Rio favelas as well as illicit gambling (Jogo do Bicho) are also said to contribute financially to schools, as many of them are guardians and controllers of shanty town life.
Source: Samba school – Wikipedia