Question: Could you say that this country was based on the work of slaves, and that it gave us an advantage over other countries?
Answer: Slavery was a huge disadvantage. It held us back, especially in the South. Obviously, slavery is a huge disadvantage to the slaves, who are part of the country, and they're then forced to live stunted lives, but also pretty much everyone else. Slavery is a dead-weight loss, both morally and economically. It caused huge social friction between North and South, between slaves and non-slaves, people who were for abolition and people who were not, as well as being economically underperforming.
The important thing to note historically is that those countries that rejected slavery and worked hard to abolish it; those are the countries that became rich first and then fastest.