The American eighteenth century was characterized by impressive population growth. In 1760, the Thirteen Colonies were home to 1,267,800 inhabitants, whereas in 1660, the first six colonies totaled only 134,000 inhabitants. Multiplied by an average of nearly 10 in a century, with rapid successes in colonies like Pennsylvania where the number of inhabitants multiplied eightfold between 1710 and 1760, this population was split up more or less equally between the New England colonies in the North (437,000 inhabitants), the central colonies (400,000), and the southern colonies (432,000).

Immigration from Europe played a large role in this population growth: it is estimated that 320,000 Europeans settled in the British colonies between 1700 and 1775, among whom one third was Irish and Scottish, one third German and Swiss, one quarter English or Welsh, and 10,000 were French Huguenots, Dutchmen or Jews of other nationalities. Due to their multicultural population of European, and not strictly English, origin, these colonies appeared as spaces of openness and freedom, where cultural mixity was not feared. Thomas Paine praised this in Common Sense written in 1776 and Michel Guillaume Jean de Crèvecoeur in his Letters from an American Farmer in 1782.

However, after 1740, immigration no longer represented the driving force behind population growth in the American colonies (there was barely a 14% rise in the number of inhabitants in the eighteenth century), whereas it was responsible for 75% of the population growth in the previous century. The causes of the population explosion in America can be found in the strong and durable natural growth. According to Benjamin Franklin, whose 1751 demographic observations were cited at the end of the century by Malthus, the population of the Thirteen Colonies doubled every 20 years, an estimation that seems but little exaggerated coming from a Philadelphian with 13 brothers and sisters, all of whom reached adulthood. Between 1760 and 1790, the population grew from 1.3 to 4 million inhabitants. There were many reasons for this natural growth: a drop in the mortality rate that had been very high when the first settlers arrived, due to epidemiological challenges (yellow fever and malaria in the south) or hard winters in the north, but ended up being lower than in Europe due to the more rural setting in a time when over-crowding in cities accelerated the spread of disease; medical progress (inoculation against small pox or mumps starting in 1721); greater life expectancy; a smaller percentage of unmarried people than in Europe (3% against Europe’s 10%); a lower marriage age to take advantage of women's reproductive years (whereas in Europe postponing marriage for more than two years on average in relation to Americans was used as a form of contraception); access to abundant grain and meat, whereas in Europe meat was only eaten by the upper classes. It was not uncommon for an American couple to have ten children for whom the parents feared neither famine nor lack of land to cultivate. At the end of the War of Independence, the American population was so young that the median age among Whites was sixteen.

Urbanization progressed in the colonies. Philadelphia, with its 35,000 inhabitants in 1760, became the most populated city in the Anglo-Saxon world after London. The number of cities with more than 10,000 inhabitants rose from two in 1720 (Boston and Philadelphia) to five in 1770 (with the development of Newport, New York, and Charleston). But even if there were more of these large cities in the eighteenth century, the Thirteen Colonies, especially the inland regions, remained mostly rural up to the War of Independence.

Thanks to of the population explosion in the 1760, the colonization of the inland regions accelerated, all the way up to Indian territory: the areas between Vermont and the Savannah River in the south, the valleys of the Ohio, the Monongahela and the Allegheny rivers to the west of the middle colonies and along the Connecticut River and the Mohawk Valley in New England were settled at a regular rhythm, benefiting from migrations from within the colonies. Before, the port cities and grain-growing valleys had been favored. Tensions appeared between the communities that had established sparse settlements in the inland regions (often members of Protestant sects like the Quakers or the Presbyterians) and the newcomers who traveled in massive numbers to cultivate the land. These areas, where there was strong diversity and rapid upward social mobility, were known as contrasted territories, deprived of stable landmarks such as well-defined parish, and concentrating vices and frustrations. In each of the colonies a dual society emerged bringing the elite from the cities along the east coast in opposition with the “new” settlers of the inland regions, who felt disregarded by the former when they often had to undertake long journeys towards the main coastal city to complete administrative procedures. Revolts against the domination of the elite in the east broke out in the 1760s and 1770s: the Regulators in North and South Carolina between 1768 and 1771 or the Paxton Boys in Pennsylvania in 1763-1764 accused the authorities of protecting the American Indians who converted to Christianity while Whites were living in misery.

The relations with the American Indians of the inlands were complex. At first, the British established cordial relations with them founded upon bartering and skillful diplomacy. Until the 1750s at the earliest, Pennsylvania or even New York maintained peaceful relations with the Iroquois league. Pressure from the population and the breach of certain alliances soon disrupted these relations. Throughout the Seven Years’ War, several Indian nations (Algonquins, Hurons) came down in favor of the French who, unlike the English, traded with them without threatening their territory. Following this new power struggle, their lands were occupied in various ways:

• Following a negotiation and/or the conclusion of a treaty: by the Treaty of Lancaster in 1774, the six Iroquois nations let the inhabitants of Maryland, Pennsylvania, and Virginia colonize the Shenandoah Valley. In the same way, in 1752 the Treaty of Logstown between the Iroquois, the Shawnees, the Delawares and Virginia authorized settlement on the southern bank of the Ohio River.

• The purchase of land by the settlers of European origin: in the 1760s, James Wright, Governor of Georgia, bought millions of hectares primarily from the Creek Indians.

• Occupation by violence: in 1760 and 1761, South Carolina waged a war against the Cherokees, that devastated the western borders of the colony, where tensions remained strong.

The case of the American Indians shows that the American colonies were not only multicultural, but also multiethnic. The presence of Blacks on the Eastern coast of America has been dwelt on at length in American historiography, which for a long time clang to a vision inherited from the Civil War, bringing the pro-slavery South in opposition to the modern and progressive North which called for the end of the slave trade and slavery. The reality was surely more complex: all the American colonies, from the north, center, and south, started out in the seventeenth century as societies with slaves (until the 1680s incidentally, the servile labor force was made up of Whites rather than Blacks, with many Irish among them), before they became in their own time slave societies in which the inferior legal status of slaves — most of them black at the end of the seventeenth century and in the eighteenth century — was essential for their economic development. Between 1670 and 1807, an estimated 3 million people are said to have been transported in the British transatlantic slave trade, but three quarters of those slaves were deported to the West Indies. The North American market therefore remained secondary (1/6 of the total) even if a portion of the deported slaves in the islands were, in the end, re-exported to the continent. Boarded onto slave ships from London, Bristol, and Liverpool in Senegambia, the Bay of Biafra, Angola, or Mozambique, the slaves most often arrived in Newport, in the Chesapeake Bay and especially in Charleston. Numerous slave ships arrived there, but half of the 1,000 ships arriving in Charleston each year from 1735 to 1775 between June and August most often carried only a dozen slaves, who were quarantined on Sullivan’s Island before being sold in the city and immediately put to work.

Starting in 1696, each colony adopted a slave code. The first one was draft in South Carolina, a colony born from slavery, and became stricter as slave revolts and escapes intensified. The legal status of slaves did progress as one moved further north: in New England courts, Blacks received the same treatment as Whites, except in cases of murder. Employed as servants or artisans, they had a greater chance of being freed, as shown by the example of Kofi Slocum, who was freed in the 1740s and whose son later gained the reputation of the “Richest Blackman” in America, or that of Phillis Wheatley, slave-servant of tailor John Wheatley’s wife, who became a poet in the 1770s. In 1790, nearly all the Blacks in the New England colonies were free, which was certainly not the case in the southern colonies: Virginia, Maryland, Georgia, and South Carolina were the largest slave buyers.

In 1776, the Revolution initiated a transition phase of which Blacks attempted to take advantage in various ways: escape, lawsuits, petitions from the Sons of Africa demanding equal rights, and enrollment in one of the two armies that promised freedom after a certain amount of service. They were assigned dangerous and/or unusual tasks, or they were stationed in an all-Black regiment or amongst the militiamen, since prejudices still ran high. Paradoxically, by enrolling in one of the two armies in an attempt to earn their freedom, the Blacks became commodities once again since slaves suspected of having escaped or of having moved over to the enemy’s side could at any moment be captured and used as loot or exchanged for money, as exemplified by the 23 slaves of Thomas Jefferson’s Virginia plantation who chose to follow General Cornwallis.