Besides defending the country from external foes such as during the Congo Crisis and battling regional insurgencies like the Rwenzururu movement, the Uganda Army was politicized. It became dominated by people from northern Uganda such as the Acholi, Langi, and West Nile tribal people. Over the course of the Mengo Crisis of 1966, Prime Minister Milton Obote and his "protégé", Uganda Army commander Idi Amin, used the military to oust the country's president, Mutesa II of Buganda, and establish a "de facto" dictatorship. This event marked the full entry of the military into the political arena, and the start of ethnic purges in the Uganda Army, as many Bantu and Teso troops were ousted from the ranks. Obote subsequently assumed the presidency and Amin was appointed head of the Uganda Army, but rifts soon emerged between the two allies. Obote feared that the Uganda Army had become too dominated by West Nile tribesmen who were regarded as partisans of Idi Amin, and reacted by ordering the recruitment of more Langi and Acholi. By 1968, the Uganda Army had been expanded to about 9,800 personnel. By 1971 it was rumoured that Obote would have Amin arrested. The rivalry culminated in Amin's successful coup d'état of 25 January 1971, when Obote was on a trip abroad. The takeover was achieved with the support of a small coterie of low ranking army officers—most of whom were of Nubian or West Nile origin—who felt their positions would have been threatened by Amin's arrest.