East Africa generally comprises the area made up of the following countries: Comoros, Burundi, Democratic Republic of Congo, Djibouti, Eritrea, Ethiopia, Kenya, Mauritius, Madagascar, Mozambique, Rwanda, Seychelles, Somalia, South Sudan, Sudan, Tanzania, and Uganda, .
The Library of Congress Subject Heading system only uses "Christianity -- [Country name]" or "Christianity -- Africa". It's very unlikely to see "Christianity -- West Africa" as a geological subheading.
Likewise, it's important to note that searching "Christianity -- Africa" will not include books whose catalog record only includes "Christianity -- [Country name]" as a subject heading -- even if that country falls within Africa.
The Freedom of the Spirit : African indigenous churches in Kenya by 
A Spirit of Revitalization : urban Pentecostalism in Kenya by 
Church, State and Colonialism in Southeastern Congo, 1890–1962 by 
Christianity, Politics, and Public Life in Kenya by 
The Origins of the New Churches Movement in Southern Ethiopia, 1927-1944 by 
Ethiopia : the living churches of an ancient kingdom by 
Migration and Christian Identity in Congo (DRC) by 
History of the Methodist Church in the Central Congo by 
Presbyterian Reformers in Central Africa : a documentary account of the American Presbyterian Congo Mission and the human rights struggle in the Congo, 1890-1918 by 
The Jesuits in Ethiopia (1609-1641) : Latin letters in translation by 
Mutira Mission : An African Church Comes of Age in Kirinyaga, Kenya (1912-2012) by 
The Presbyterian Church of East Africa : an account of its Gospel Missionary Society origins, 1895-1946 by