Answer:
42% (During the civil war period)
Explanation:
The north had a much higher population, as it was more densely populated with big cities, while the south was plantations and farmland.
The North had a population of about 20 million and the South about 9 million.
Actually, slaves made up around 43% of the Southern population.
The slave population among "border states" was not significant.
Delaware as example had less than 1,000.
