Lagos - For Oscar-nominated British actor Chiwetel Ejiofor, starring in a film about Nigeria's civil war was "incredibly personal", as the conflict both affected close relatives and determined the country where he was born.
His own grandfather had lived through the nightmare played out in "Half of a Yellow Sun", which premiers in Nigeria on Friday, and spent long hours years later recounting the painful memories to Ejiofor.
While the actor won his Academy Award nomination for "12 Years a Slave", 2014's Best Picture winner, he said he felt particular "connective tissue" with the lead character in the Nigerian war film.
The movie -- now showing in Britain and Australia and opening soon in the US and other countries -- is based on the best-selling novel by Chimamanda Ngozi Adichie about the 1967-1970 Biafra War, which began after the eastern region tried to secede from newly independent Nigeria.
"The Biafra War was a seminal part of my upbringing and my family history," said Ejiofor, 36, the first black actor from Britain nominated for a Best Actor Oscar.
"In fact, I would say that the Biafra War was the reason I was born in London and not in Nigeria," he told journalists in Lagos earlier this month.
His parents, natives of eastern Nigeria, left the country after the horrific conflict that killed more than one million people, including many from starvation.
The war was a regular family discussion topic throughout his upbringing in London, but Ejiofor said he acquired a fuller understanding of the conflict during a visit to Nigeria six years ago.
At independence from Britain in 1960, the country was divided into three geopolitical zones: the north, dominated the mainly Muslim Hausa tribe, and two predominantly Christian regions, the west where the Yoruba were the majority and the east, led by the Igbo people.
In 1967, Igbo leaders declared independence after claiming that their tribesman living in the north were being massacred by Hausas. They charged the federal government with failing to provide protection.
Ejiofor's maternal grandfather was among the Igbos based in the north during those violent, chaotic years.
The actor said he recorded 10 hours of conversation in Nigeria with his grandfather -- who died three years ago -- and played the material for "Half of a Yellow Sun" director Biyi Bandele and other cast members.
"It was an extremely powerful and moving account of an ordinary Igbo man in the north," Ejiofor said.
"An ordinary Nigerian experiencing this extraordinarily turbulent time, from the hope of independence to the seismic cost of the war."
The attempt to create an Igbo-led republic was crushed by the British-backed Nigerian federal forces, who had military superiority and used scorched earth tactics, including the blockage of all food imports to the breakaway Biafra region.
In "Half of a Yellow Sun", Ejiofor plays Odenigbo, an idealistic math professor at the University of Nigeria in the eastern town of Nsukka.
Odenigbo hosts colleagues and friends for long-nights of drinking and discussion about Nigeria's immense promise following the dismantling of colonialism.
His dreams are destroyed by the massacres and ultimately by the civil war.
"I had Chiwetel (Ejiofor) in mind for the part of Odenigbo," Bandele told AFP.
"I did not have to audition him. I knew that he was going to be perfect. And he was."
"Half of a Yellow Sun", produced by Andrea Calderwood who also made "The last king of Scotland" about the Ugandan dictator Idi Amin, was filmed entirely in the southeastern Nigeria city of Calabar and a nearby village called Creek Town.
The latter half of the film, which unfolds after the Biafra War has broken out, was shot first and the cast's war-ravaged look was a product of more than just make-up and strong acting, Bandele said.
"Some of us had typhoid," and likely contracted it on the first day of filming in Creek Town, he said.
"People started falling like flies three days into the shoot."
Female lead Thandie Newton was among those who got sick and looked like "something the cat dragged into the house."
"And it's because she had typhoid! And her character is supposed to be going through a tough time here, so it actually worked really well!" Bandele said.
"I mean I wouldn't recommend that as a way of making movies, but it worked, it really worked for us."