What evidence was available in 1820 to support jefferson's point of view; and what trends had already begun to emerge that would lead the intensification of the conflict over slavery in the decades to come?

The Missouri Compromise where it was declared as a slave state and separated from the free state. Although in the 17th century Britain has already declared the illegal issued of the slave trade, America did not stop having their own slaves that helped with the production in agriculture and industries. The segregation did with black people made them have the push to fight for their freedom. A lot of people had involved themselves in this intensified fight for their racial and social freedom as human beings.