Question

What do you think spiegel means by the "horrors of slavery"?

Answer 1

Slavery was never a good thing, and for the slaves it was scary. So by saying "The horrors of slavery" Spiegel is just saying that slavery was a horrible thing.

Answer 2

Although slavery is evil and bad, no matter what, this was a very specific matter that Spiegel was talking about. When he talked about "horros of slavery", he was talking about the soldiers who were enslaved to the American Army. Spiegel believed that he was doing his duty to his country, family and God as a citizen, but he also believed that it such a thing should always be his choice,  not the government's choice at all.