Crispus Attucks being shot during the Boston Massacre.
(John Bufford after William L. Champey, circa 1856)[6]
African Americans were an integral part of the revolutionary war for the Americans. They served as soldiers, guides, messengers and spies. They fought in key battles for the Americans such as in April 1775 at Lexington and Concord as well as The Battle of Bunker Hill. Whether the African Americans were enslaved or not, many of them wanted to fight for the Patriots with the idea that it may lead to freedom or more rights.
http://en.wikipedia.org/wiki/African_Americans_in_the_Revolutionary_War#African_American_Patriots
Image of Black Loyalists in the American
Revolution.
The British did use African Americans as laborers, skilled workers, foragers and spies. Except for those blacks who joined Lord Dunmore's Ethiopian Regiment, there were only a few blacks who served in the British army while the fighting was concentrated in the North. It was not until the final months of the war, when manpower was low that blacks were used for fighting for Britain.