The first missionaries arrived in Tanzania with the Portuguese, in the 15th century, but true evangelization only began in 1867 with the Fathers of the Congregation of the Holy Spirit. The latter immediately consecrated the mission to the Immaculate Heart of Mary.
In 1948, the pilgrimage of the statue of Our Lady of Fatima was greeted triumphantly. The Muslims even joined in the prayers: the great Sultan Sayyd Khalifah ibn Harub of the city of Zanzibar (a city with 25 mosques) offered an immense bouquet of carnations. In Dar Es Salaam, a crowd of pagans and Muslims welcomed Our Lady with enthusiasm.
In 1955, many Catholic families participated in the Rosary Crusade.
The current government has a plan to totally Islamize the country, disrupting Christian and Muslim relations, which have long been peaceful.
See Attilio GALLI, Madre della Chiesa dei Cinque Continenti, Ed Segno, Udine, 1997, p. 747-753