Final answer:
Pennsylvania's forward thinking led the way in fighting against slavery with a gradual emancipation law.
Step-by-step explanation:
The colony that' s forward thinking led the way in fighting against slavery was Pennsylvania. In 1780, Pennsylvania passed a law outlining a process of gradual emancipation, stating that children born to slave mothers after March 1, 1780, would be considered indentured servants and freed at the age of 28. This law was a significant step towards ending slavery in the United States.