With the invention of the cotton gin (a piece of machinery used in cotton production) more workers were needed to operate these machines so the demand for labour was high. While the cotton gin was revolutionising the rural life in south America ( I hasten to point out that most of the southern lands I speak of were not states at this time, and were a relatively recent 'discovery') an industrial revolution was occurring in the north. The north's climate was not suitable for growing cotton, so the northerners relied on a thriving secondary industry. With the recent advancement in industrial technology the work force in the north was getting smaller compared to demand. Slaves would be the perfect answer to the south's problem of lack of work force: they could be injected straight into the population with a relatively minute wait, they needed no sanitary condition working and non-working and they would do it all for free. While many places legalised slavery others decided it was immoral.
Here is a brief timeline:
1641 Massachusetts Bay Colony legalises slavery.
1660 Virginia legalises slavery.
1663 Maryland becomes the first colony to enact laws that recognise slavery for life. Under prior English law slaves who became Christians were granted freedom.
1667 Virginia passes a law revoking the prior English law that allowed for slaves that converted to Christianity to become free.
February 1688 The first organised protest against slavery in the new world was drafted by a group of Quakers in Germantown, PA. Known as the Germantown Protest, it argued that Christians should do as they would want to be done to them, that slavery was essentially theft as you were buying something stolen and that adultery is wrong yet slave traders/owners forced adultery on men and women by breaking up marriages when they resold husbands and wives to different owners. How could as Christians, could such actions be condoned?
This is just a small sample of events that occurred around that time. With the legalisation of slavery two basic ethos' appeared, one stating that slavery was a cruel and barbaric practice that should be abolished whereas the other stated that slavery was needed for America's economy and that it wasn't that cruel or barbaric and that it should be allowed to continue.
The former ethos was adopted by the north whereas the later was taken on by the south. The northerner argued that you could get a worker for cheaper and without having to house and cloth them by hiring people without going into slavery, the south said that slavery could be kinder than normal work and took examples of particularly kind slave owners.