Africans were also used in large numbers for slavery because they were easier to buy. During the beginning of the Atlantic Slave Trade, Africans were willing to sell other Africans as slaves to Europeans because they had their own system of slavery.
You could have sex towards the end of your bleeding and then actually conceive 4 or 5 days later with your early ovulation. The probabilities of getting pregnant while on your period are low, but the possibilities are there. This is not the time to have sex if you are trying to get pregnant.
You may or may not get your period while pregnant. A lot of women don't have it...but there are a few that do still get it. Yes, you can have sex all you want while you are pregnant as long as the doctor doesn't tell you otherwise and you don't react badly to it.