The kingdom of Kongo was governed in concert by the Mwene Kongo and the royal council known as the ne mbanda-mbanda, roughly translating as "the top of the top". It was composed of twelve members divided into three groups. One group were bureaucrats, another who were electors and a last of matrons. Senior officials chose the Mwene Kongo or king who served for life following their choice. Electors varied over time, and there was probably never a completely fixed list; rather, senior officials who exercised power did so. Many kings tried to choose their successor, not always successfully. One of the central problems of Kongo history was the succession of power, and as a result, the country was disturbed by many rebellions and revolts.