The correct answer to this open question is the following.
Although there are no options attached, and there is no context or further references, we can say the following.
It seems that here we are talking about the Underground Railroad.
If this is the case, the more important achievement could have been conducting slaves to freedom over a long period.
And we have to take into consideration that these people that helped them put their lives at risk. So knowing this, they risk themselves for a good cause. They were northern people that believe in integration and wanted to free black slaves from the oppression of the South.
The Underground Railroad was the name of the people and the system they use to help slaves to enter the northern territory before the beginning of the American Civil War. They did that for 30 years.