Argentina is a federation of 23 provinces and the federal capital of Buenos Aires. During the 19th century there was a bitter struggle between Buenos Aires and the interior provinces, and there has long been an element of tension regarding the division of powers between the central government and provincial bodies. The federal government retains control over such matters as the regulation of commerce, customs collections, currency, civil or commercial codes, or the appointment of foreign agents. The provincial governors are elected every four years.
The constitutional "national intervention" and "state of siege" powers of the president have been invoked frequently. The first of these powers was designed to "guarantee the republican form of government in the provinces." Since the adoption of the 1853 constitution, the federal government has intervened over 200 times, mostly by presidential decree. Under this authority, provincial and municipal offices may be declared vacant, appointments annulled, and local elections supervised. Between 1966 and 1973, all local legislatures were dissolved and provincial governors were appointed by the new president. A restoration of provincial and municipal government followed the return to constitutional government in 1973. After the March 1976 coup, the federal government again intervened to remove all provincial governors and impose direct military rule over all municipalities. Since 1983, representative local government has been in force again.
Until 1996, the President appointed the mayor of Buenos Aires, and by law, the president and Congress controlled any legislation that affected the city. Constitutional reforms that year led to an elected mayoral position, and a 60-member Poder Legislativo (legislative power). The members are elected by proportional representation to four-year terms.