Answer: The central idea is about slaves getting the freedom to the North using underground railroads.
Explanation: The main idea is about slaves getting freedom to the North using underground railroads. In the 1850s and 1860s, in the United States, states in the South practiced slavery while states in the North did not allow for slavery. This led to establishing of the underground railroad as a secret passage for slaves to escape from the South to go to the North in search of freedom.