Free blacks in the North and South fought on both sides of the Revolution, but most fought for the colonial rebels. Crispus Attucks, who died in a conflict in Boston in 1770, is considered the first martyr of the American Revolution. Both sides offered freedom and re-settlement to slaves who were willing to fight for them, especially targeting slaves whose owners supported the opposing cause.
Many African-American slaves became politically active during these years in support of the King, as they thought Great Britain might abolish slavery in the colonies. Tens of thousands used the turmoil of war to escape, and the southern plantation economies of South Carolina and Georgia especially were disrupted. During the Revolution, the British tried to turn slavery against the Americans, but historian David Brion Davis explains the difficulties with a policy of wholesale arming of the slaves:
But England greatly feared the effects of any such move on its own West Indies, where Americans had already aroused alarm over a possible threat to incite slave insurrections. The British elites also understood that an all-out attack on one form of property could easily lead to an assault on all boundaries of privilege and social order, as envisioned by radical religious sects in Britain’s seventeenth-century civil wars.
Davis underscored the British dilemma: "Britain, when confronted by the rebellious American colonists, hoped to exploit their fear of slave revolts while also reassuring the large number of slave-holding Loyalists and wealthy Caribbean planters and merchants that their slave property would be secure. The colonists accused the British of encouraging slave revolts.
American advocates of independence were commonly lampooned in Britain for what was termed their hypocritical calls for freedom, at the same time that many of their leaders were planters who held hundreds of slaves. Samuel Johnson snapped, "how is it we hear the loudest yelps for liberty among the slave drivers of the Negroes?" Benjamin Franklin countered by criticizing the British self-congratulation about "the freeing of one Negro" (Somersett) while they continued to permit the Slave Trade.
Phyllis Wheatley, a black poet who popularized the image of Columbia to represent America, came to public attention when her Poems on Various Subjects, Religious and Moral appeared in 1773.
During the war, slaves escaped from across New England and the mid-Atlantic area to British-occupied cities, such as New York. The effects of the war were more dramatic in the South. In Virginia the royal governor Lord Dunmore recruited black men into the British forces with the promise of freedom, protection for their families, and land grants. Tens of thousands of slaves escaped to British lines throughout the South, causing dramatic losses to slaveholders and disrupting cultivation and harvesting of crops. For instance, South Carolina was estimated to lose about 25,000 slaves, or one third of its slave population, to flight, migration or death. From 1770-1790, the black proportion of the population (mostly slaves) in South Carolina dropped from 60.5 percent to 43.8 percent; and in Georgia from 45.2 percent to 36.1 percent.
When the British evacuated its forces from Charleston, it also gave transportation to 10,000 slaves, carrying through on its commitment to them. They evacuated and resettled more than 3,000 "Black Loyalists" to Nova Scotia, Upper and Lower Canada. Others sailed with the British to England or were resettled in the West Indies of the Caribbean. More than 1200 of the Black Loyalists of Nova Scotia later resettled in the British colony of Sierra Leone, where they became leaders of the Krio ethnic group of Freetown and the later national government. Many of their descendants still live in Sierra Leone, as well as other African countries.
Some slaves understood Revolutionary rhetoric as promising freedom and equality. Both British and American governments made promises of freedom for service, and many slaves fought in one or the other armies. Starting in 1777, northern states started to abolish slavery, beginning with Vermont, which ended it under its new state constitution. By court cases, Massachusetts effectively ended slavery before the end of the century. Usually states instituted abolition on a gradual schedule with no government compensation of the owners, and many states, such as New York, New Jersey and Connecticut, required long apprenticeships of former slave children before they gained freedom and came of age as adults.
In the first two decades after the war, the legislatures of Virginia, Maryland and Delaware made it easier for slaveholders to manumit their slaves. Numerous slaveholders in the Upper South took advantage of the changes: the proportion of free blacks went from less than one percent before the war to more than 10 percent overall by 1810. In Virginia alone, the number of free blacks climbed: from less than one percent in 1782, to 4.2 percent in 1790, and 13.5 percent in 1810. In Delaware, three-quarters of blacks were free by 1810. After this time, few slaves were freed in the South, except those who were favorites or the master's children. The demand for slaves rose with the growth of cotton as a commodity crop, especially after the invention of the cotton gin, which enabled the widespread cultivation of short-staple cotton in the upland regions. Although the international slave trade was prohibited, the slave population in the United States increased by the formation of families and survival of children throughout the South. As the demand for slave labor in the Upper South decreased due to changes in crops, planters began selling their slaves to traders and markets to the Deep South in an internal slave trade; it would cause the forced migration of an estimated one million slaves during the following decades, breaking up countless families, as young males were most in demand.