In today's politically correct world, it is inconvenient to discuss our ancestors in their historical context. We have been doing research about our New England ancestors, particularly those in Rhode Island. One family tradition relates that a prominent ancestor, possibly William Tanner, was arrested in England and transported to New England as a transported convict. One interesting article on the subject is the Wikipedia article, "Penal Transportation." The number of convicts transported has apparently never been firmly established. But estimates run as high as 120,000 or more.
We have found that genealogists in the U.S. are often not willing to consider that their "immigrant" ancestor was actually a felon and transported involuntarily. Upon arriving in America, it was easier than in England to simply "run away" with a new name and new identity.
The distinction between a slave and an indentured servant was one of time constraints. The term of servitude for an indentured servant was usually seven years, the same time that transported convicts served. Estimates are that from the earliest years until the American Revolution, half to two-thirds of the immigrants to the colonies were indentured. See Wikipedia: "Indentured servitude in the Americas." Both transported and indentured ancestors can present some challenging research situations.
Slaves constitute another major category of arrivals in North America. In our day it is viewed as an African American issue, however, there were white and Native American slaves also. Researchers who have "New England" ancestors often fail to consider that their ancestors may have been slaves or slave owners. This recently came up in our own family's research when the Tanners were shown to be slave owners in Rhode Island. In fact, Rhode Island, at one point, had the highest percentage of slaves in the population of any of the northern colonies. See "Slavery in Rhode island."
The incidence of all three categories of people mandates that genealogical researchers be open to the possibility of having one or more of these categories in their own ancestral lines.
Here are a few more books for reference:
Alderman, Clifford Lindsey. Colonists for Sale: The Story of Indentured Servants in America. New York: Macmillan, 1975.
Blackmon, Douglas A. Slavery by Another Name: The Re-Enslavement of Black People in America from the Civil War to World War II. New York: Doubleday, 2008.
Blashfield, Jean F. Slavery in America. New York: Children’s Press, 2012.
Campbell, Ciara. Slavery in America, 2016. http://public.eblib.com/choice/publicfullrecord.aspx?p=2101649.
Christianson, Scott. With Liberty for Some: 500 Years of Imprisonment in America. Boston, MA: Northeastern University Press, 1998.
Coldham, Peter Wilson, and Genealogical Publishing Co. “British Emigrants in Bondage, 1614-1788.” Genealogical Pub. Co., 2005.
Drake, Thomas Edward. Quakers and Slavery in America. Ann Arbor, Michigan: University Microfilms International, 1980.
East Yorkshire Family History Society. Transportation: From Hull and the East Riding to America & Australia Taken from Quarter Session Records. Hull] ([104 The Parkway, Willerby, Hull, N. Humberside HU10 6BE]): East Yorkshire Family History Society, 1984.
Hollander, Barnett. Slavery in America. New York: Barnes and Noble, 1964.
Liston, Robert A. Slavery in America: The History of Slavery. New York: McGraw-Hill, 1970.
Miller, Wilbur R. The Social History of Crime and Punishment in America: An Encyclopedia. Thousand Oaks, Calif.: SAGE, 2012. http://site.ebrary.com/id/10682676.
Morgan, Gwenda, and Peter Rushton. Banishment in the Early Atlantic World: Convicts, Rebels and Slaves. London: Bloomsbury, 2013. http://public.eblib.com/choice/publicfullrecord.aspx?p=1190713.
Raskin, Joseph, Edith Raskin, and William Sauts Bock. Tales of Indentured Servants. New York: Lothrop, Lee & Shepard, 1978.
Schneider, Dorothy, and Carl J Schneider. Slavery in America. New York: Facts On File, 2007.
———. Slavery in America. New York: Facts on File, 2008. http://ebooks.infobaselearning.com/View.aspx?ISBN=9781438108131&InstId=7667.
Wareing, John. Emigrants to America: Indentured Servants Recruited in London, 1718-1733. Baltimore, Md.: Reprinted for Clearfield Co. by Genealogical Pub. Co., 2002.
———. Indentured Migration and the Servant Trade from London to America, 1618-1718: “There Is Great Want of Servants,” 2017.
Wokeck, Marianne Sophia. Trade in Strangers: The Beginnings of Mass Migration to North America. University Park, Pa.: Pennsylvania State University Press, 1999. http://search.ebscohost.com/login.aspx?direct=true&scope=site&db=nlebk&db=nlabk&AN=25473.