Slavery had existed in North America since the Spanish arrived, but slavery involving blacks from Africa was begun by the Dutch. By the time of the Revolution it was an ingrained part of the economy. There was, for a brief period at the end of the Jacobite Wars in Britain, a trade in abducted white people usually from the border areas of Scotland being sold as slaves to planters in the New World.
Slavery had been an accepted part of human culture and economy from the most ancient times, and so most people did not view it as anything out of the ordinary. Slavery existed in all of the colonies and the early states. The first black slaves in America were traded by the Dutch to the British settlers in Jamestown in Virginia in 1619, but they were treated as indentured servants and given their freedom after working for a period of years equivalent to most indentured servant contracts. That changed as time went on. In 1640 Maryland legally institutionalized slavery, but the concept of slaves as chattel property in America began in 1641 with the "Body of Liberties" legislation in Massachusetts.
Although we have the stereotype of the Southern slave-owner and the Northern Abolitionist, the institution of slavery as it became known in American culture through the 18th century was actually a product of the legislatures and social leadership of the Northern colonies. The Abolition Movement as we tend to view it did not begin until much later, and was never popular among the working classes of the North. Although Cotton Mather advocated the education of blacks, he also believed they were destined to be slaves by their natures. This view was widely held even among the organizations and individuals who advocated education and humane treatment of black slaves. The preponderence of slaves in the South came about gradually, and only after the invention of the Cotton Gin made the mass production of cotton economically viable. Until then slavery was as common in the North.
The concept of slavery seems antithetical to many of the reasons why Europeans came to the New World, and this was obvious to these people. To justify the practice an ideology of black inferiority was developed. Again contrary to our modern stereotypes, this philosophy was developed in the Northern colonies, although Southerners were certainly susceptible to these ideas. Later, when the large Southern plantations became dependant on slavery, this caused great ambivalence (the word meaning "strong feelings both positive and negative"). There are many records of the struggle of slave owners with this problem of conscience.
One of the links below leads to an account written by a freed 18th century slave named Olaudah Equiano, also known as Gustavus Vassa. This is a unique first-person account of 18th century life as a slave in both Africa and the New World.