Who discovered America?

For Europeans Columbus discovered the 'Americas' in the Caribbean, Central, and South America (1492-1502). If you mean the part of North America that would be the US, John Cabot an Italian sailing for England discovered it (1498).

Paleo Indians and Vikings were not 'explorers' who 'discovered' anything, they did not set out to find anything, did not return home to report a discovery, but instead were migrants/ settlers looking for new lands to settle in.

Modern times Lief Erickson John Cabot his men Explored as the Great lakes and Maine

The first fully recorded discovery of America, were the when the Norsemen came to America.

But technically before that were the Indians, which were already there in the first place.

The first Asians who crossed the land-bridge from Siberia tens of thousands of years ago.

Paleo-Indians migrated from Eurasia to what is now the U.S. mainland around 15,000 years ago.

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The Vikings.