They came from their own countries and, using black slaves, built some infrastructure.

They did not come using slaves, that makes no sense at all. Slaves were unskilled manual labor, they never empowered anyone to do anything they couldn't already do. Slaves were not used to build infrastructure. They were used on plantations and as house servants.

Slavery was not brought into the colonies until long after the colonies were established. Settlements were built by settlers.

Who were in their own country.

What country was that?

The natives lived in tribes. The tribes did not recognize any land ownership. They regularly went as far as they wanted and killed any other natives they came across. They killed settlers as well, but quickly learned that white settlers had guns and were too strong to be killed like other tribes. They never established any country. That was a concept that white men brought to the continent. And according to the white man's customs they bought the land from the natives who were on it, only for the natives to take the payment then completely ignore that treaty and continue to try pushing settlers off the land they bought.

No settler ever took over any city that natives had built because natives never built any cities. They had temporary camps which were completely useless to settlers because of the poor quality of the buildings. Everything the settlers had they built. And they built a great country from the ground up. Only then were slaves brought in, by jewish merchants, to sell as manual labor for farms.