What is slavery
and why did it happen

Slavery is the practice of owning slaves (workers who are treated poorly and don't make any money, forced labor). It still continues on today so there is no such thing as "did" but I think mostly because it is free labor. Slavery is still practiced all around the world today.

abraham lincoln  (february 12, 1809  – april 15, 1865) was an american statesman, politician, and lawyer who served as the 16th  president of the united states  from 1861 until  his assassination  in april 1865. lincoln led the nation through the  american civil war, its bloodiest war and its greatest moral, constitutional, and political crisis.[2][3]  he preserved the  union,  abolished slavery, strengthened the  federal government, and modernized  the u.s. economy.

woah dude who's thia? need more info