Unstable reign in African country (5)
I believe the answer is:
niger
'african country' is the definition.
(country in Africa)
'unstable reign' is the wordplay.
'unstable' indicates an anagram.
'reign' with letters rearranged gives 'NIGER'.
'in' acts as a link.
(Other definitions for niger that I've seen before include "Country in interior of N Africa, capital Niarney" , "Landlocked W African republic" , "Major West African river" , "River of West Africa" , "West African river and country" .)