So Long a Letter is set in the time around the historical independence movement in the African nation of Senegal. The narrator, Ramatoulaye Fall, has lived through the tumultuous times of revolution and has those experiences added to her own experience as a normal woman living in Senegalese culture. Like the historical aspects of history, Ramatoulaye's own life is split into "historical" portions, from her life as a married woman to a widow, and her refusal to marry again. She contrasts this with the real-life history that occurs around her:
It was the privilege of our generation to be the link between two periods of our history, one of domination, the other of independence... we witnessed the birth of a republic, the birth of an anthem and the implantation of a flag.
(Mariama Bâ, So Long a Letter, Google Books)
Senegalese independence came after centuries of European colonialism, with the indigenous people enslaved, sold, or simply brutalized by Europeans in the manner of the time. During the 1900s, Senegal and its neighbor nation Mali (formerly the French Sudan) merged to create the Mali Federation, declaring their independence from European control. However, they split apart again in 1960, and Senegal became an entirely independent nation. Since the novel was published in 1980, it precedes the 1982 merge of Senegal with The Gambia, which later dissolved. Therefore, the time period of the novel is between 1960-1980.