According to UNESCO, some 30 million Africans were forcibly uprooted from their homeland during the 400 year span of the transatlantic slave trade.
Considered to be the largest forced displacement of people in history, slavery and the transatlantic slave trade have only recently been recognized by the international community as crimes against humanity.
Since 2005, 25 March is observed as the International Day of Remembrance of the Victims of Slavery and the Transatlantic Slave Trade. People the world over pay tribute to the victims of the abhorrent commerce in humans and vow to abolish these crimes once for all.
http://www.ohchr.org/EN/NewsEvents/Pages/SlaveryInternationalDay.aspx