I came of age in the 1960’s and the Biafra genocide was a major news story for about two years.
From memory.....
A large share of the 3 million dead were from starvation and child disease deaths caused by refugee issues and systematic terror and the extreme logistic difficulties in Africa.
As I recall, the UK was the Nigerian colonial power, and violence started almost immediately after Independence and the UK presence disappeared.
The Muslims were in the north part of Nigeria, and were much poorer and less Westernized.
In the south, and especially along the coast, people were much more prosperous and Westernized and many were Christian.
The port cities, as I recall, were actually in the slave trade for close to 300 years.
It would be an error to claim that this war was strictly Muslim versus Christian.
It's more accurate to say it was a Muslim war against non-Muslims.
Southern Nigeria has many ethnic groups and many religions.
But it's possible that Christians had the highest death toll.
I have no recollection of how or when this was all resolved.
I really hadn't thought about Biafra for years until Muslims and others recently started attacking Nigeria's oil industry, which I think is almost completely offshore.
I read a summary of the Biafra conflict at one of the Conservative blogs, and I realized for the first time that much of it was Muslims slaughtering Christians, something completely absent from the news reports 40 years ago.