Cultivating tobacco and sugar was backbreaking work, and the English landowners wouldn't do it themselves, so they got other people to work for them.
Indentured servants were people from England who would try their luck in America. For passage over the Atlantic Ocean, seeds, and sometimes land, they would sign an indenture, which basically meant that they would be servants for a specific time. However, this didn't work for one reason: the indentured servants would leave, and the landowner would need to get more.
This brings us to our next point, Indian slaves. The obvious next step for landowners was to get people to work for them nonstop. They enslaved Indians, but there were three problems with this plot. The first was that the Indians knew the land well and frequently escaped. Indians were very susceptible to European diseases, and many died because of this cause. Furthermore, Indians had well-connected families and anyone taking an Indian slave would be in danger of retribution from his family.
In 1619, a handful of African slaves arrived in Jamestown. However, African slaves were expensive because the Royal African Company was the only company exporting slaves, and they were jacking up the prices. However, when the Crown broke the company's monopoly, these slaves became cheap and were the preferred long-term labor source because they were immune to many of the same diseases as the Europeans, were far from home, and were used to growing many of the crops that their masters wanted them to grow.