Green, Martin. The Earth Again Redeemed: May 26 to July 1, 1984, on This Earth of Ours and Its Alter Ego
Divergence: 1665 CE
What if: King Antonio defeated the Portuguese invading the Kongo at Mbwila in 1665.
Summary: Interaction of two worlds diverging from the battle, one with the Congo at the heart of Christianity and one like ours but post-nuclear war.
Published: Basic 1977 (0465017622BUY); Sphere 1979.