Réponse :
How did slavery START? (/!\ l'auxiliaire prend déjà la marque du prétérit).
Sometimes during 1619
How were the Africans treated?
They were treaty very badly. They worked all day long, all week long. They were punished (whiping, beating, burning, rape...). Just the trip itself from Africa to the USA was horrible: some even died in the ships. They lived in small shacks...
Explications :
You could watch/read 12 Years a slave, when older! :)
You could also visit some museums.
You could just read and get informed on the internet, there are a lot to read, to learn :-)
