There were 13 colonies which separated themselves from England. Half had slavery. The war to succeed from England was not over slaves, but rather over taxation and representation. The issue of slaves, which distasteful, was further hindered by the fact that indentured servants were essentially slaves who in return for passage to America owed 3-7 years in return for voyages. Slavery was a legal part of the very fabric of the founding of the colonies, and this is the legacy from Spain, The Netherlands, France, Portugal and England in the expansion into the New World. America essentially inherited Slavery from the Old World. It took Americans 85 years to outlaw slavery, and another 80-years to enact equal rights for voting and women.
Slavery was legal in all of the original 13 colonies. Vermont outlawed it in its original 1777 constitution when it seceded from New York, but Vermont wasn’t admitted as a state until 1791. New York, itself, outlawed slavery in 1780, as I recall.
Ben Franklin was indentured to his own brother! I forget why.