In rural districts, slave labor displaced free labor, and in the cities servants multiplied with the concentration of wealth.

The size and character of the slave population eventually became a perpetual menace to the State.
Insurrections proved formidable, and every slave came to be looked upon as an enemy to the public.

It is generally conceded that the extension of slavery was a primary cause of the decline and fall of Rome.

In the American controversy, therefore, the lesson to be drawn from Roman experience was utilized to support the cause of free labor.
After the Middle Ages, in which slavery under the modified form of feudalism ran its course, there was a reversion to the ancient classical controversy.

The issue became clearly defined in the hands of the English and French philosophers of the seventeenth and eighteenth centuries.