What led to the adoption of slavery in the American colonies?

Slavery was already an acceptable practice in England at the time North American colonization. The initial wave of British settlers struggled to survive and were only able to remain because of help from Native Americans. Some of this help was actively given, while some help was unintentional: the massive depopulation of Native Americans due to introduced illnesses left unoccupied homes that settlers could appropriate without using force and small scale agricultural areas where food was growing but went unharvested. After the settlements became more robust and stable, the settlers began to engage in larger-scale agriculture.
Large-scale agriculture was desirable for England because it led to wealth and resources that would be shipped back to England. In order to maximize the wealth available from agriculture, the colonists began to enslave Native Americans in some areas. However, Native Americans lacked resistance to a number of European diseases, causing many to die. This led to a shift towards the enslavement of Africans, who often did have resistance to many European diseases.
The development of slavery in the American colonies was the result of a need for laborers and the lack of sufficiently robust options in the colonies themselves. Slaves often worked alongside indentured servants, though these were less favorable to masters because the expiration of the indenture could lead to burdens for the owner.