The United States blockaded the South when they tried to leave the Union; maybe that is where the Nigerian federal government learned the practice.
Some estimates - 3 million.
Biafra State Coalition Reactions To Islamic Jihad-Religious War Declared By Boko Haram
08 January 2012
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Since independence, Nigeria has had a civil war in which 3 million people died, mostly of Eastern Nigeria.
http://elombah.com/index.php/articles-mainmenu/9381-biafra-state-coalition-reactions-to-islamic-jihad-religious-war-declared-by-boko-haram-v15-9381