Saibou then secured his nomination by the Supreme Military Council as Kountché's successor, subsequently sending military rivals overseas with diplomatic tasks, and establishing the National Movement for the Development of Society (MNSD) as the sole political party in Niger.
In addition to being the Secretary-General of the MNSD, Salissou was also President of the MNSD section in Tahoua Region.
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A special congress of the MNSD-Nassara held in Zinder on 21 February 2009 elected Oumarou as the party's President; on the same occasion, Interior Minister Albadé Abouba was elected as Secretary-General to replace Salissou.
A special congress of the MNSD-Nassara held in Zinder on 21 February 2009 elected Prime Minister Oumarou to succeed Amadou as MNSD President.
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In early August 2008 Zinder and Tillaberi sections of the MNSD proposed that Amadou be removed as party President.
Along with Mamadou Tandja, the President of the National Movement for the Development of Society (MNSD-Nassara), and André Salifou, the President of the Union of Democratic and Progressive Patriots (UPDP-Chamoua), Assoumane was arrested on 17 April 1994 following a protest against the government.
In 2004 he was named as an accomplice in the 26 January murder of ruling MNSD party activist Adam Amangue in Tchirozerine.