American Free Slave State?

While slavery was still legal in the south, there were a number of slave revolts. Some were lead by slaves, others by northerners. What point in history would be most likely to produce a successful independent state in the US lead, in major part, by former slaves? What sort of person would be the ideal leader?
 
Highly unlikely that an 'Free Slave State' would be permitted or tolerated. The creation of such could spark an war between the states.
 
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