Which country was the first to bring slaves to North America?
The answer to this depends on what you mean by “bring slaves to North America.” There are at least three possible answers.
If you consider Mexico and the Caribbean to be part of North America, then Spain was clearly the first country to bring slaves to North America. The Spanish at first tried to enslave native peoples of the Caribbean. When that did not work very well, they brought in some African slaves. African slavery was not a huge part of the Spanish colonies’ economies, but the Spaniards did bring slaves to the Caribbean and New Mexico before the English had colonies in North America.
If you are only asking about the part of North America that is now the United States, the answer could still be Spain. At least one African who was enslaved by the Spanish made it to what is now Florida, Texas, and New Mexico. He is known by the name Estevanico and he reached what is now the US with Spanish explorers.
If you do not consider one or two slaves to count for the purposes of this answer, there are still two other possibilities. The first slaves known to have been brought to English North America were brought by a Dutch ship to Jamestown in 1619. This brings up the issue of who, in your view, “brought” those slaves. Were they brought by the Dutch because that is who owned the ship or were they brought by the English because the English bought them and put them to work as slaves? Either of these is a plausible answer.
So, you need to pick which of these options seems like the right answer as you understand the question.