Did the "American" Colonist Secede From the British With an All Voluntary Army?

Miscellaneous History
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Or was there something else?

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Just some things:

Upon the signing of the Declaration of Independence, 20 percent of America’s population was enslaved(500,000).

During the Revolutionary War, Washington recruited free blacks into the Continental Army, and by the time of the Battle of Yorktown, African Americans constituted 25 percent of the army.