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Several, in fact! There were at least 5 groups from outside the Americas almost universally accepted to have contacted the Americas before Columbus.

Some geographical background: America isn’t quite as far from the ‘Old World’ as you may think. At its closest point to Asia, the Bering Strait, North America is separated from Asia by only 52 miles of water. Even more conveniently, the Diomede Islands straddle the strait, serving as convenient waypoints on any overseas journey between them. But the Bering Strait is in a fairly remote area of the world and is thousands of miles removed from any ancient Civilization.

The Pacific Ocean, which divides the Americas from Asia, is massive, but not completely empty. The Southern Pacific in particular contains hundreds of small islands. These would be gradually colonized by humans between the First Millennium BC and early Second Millennium AD, as Polynesian navigators made use of improved sailing technology. The nearest Polynesian island to South America is Rapa Nui (alternatively ‘Easter Island’), still over 2000 miles away from South America but nonetheless far closer than any other Pacific landmass.

The Atlantic Ocean, which divides the Americas from Europe and Africa, is a similarly great obstacle to cross, and there was no African or European analogue to the Polynesians capable of long distance Atlantic voyages before Columbus. But in the Northern Atlantic, the large islands of Iceland and Greenland serve as natural waypoints for any prospective voyager.

All three of these routes: The Bering Strait, the Polynesian Islands, and Iceland and Greenland, would all be used to reach the Americas before Columbus.

The first ever group to reach the Americas were the ’Proto-Amerindians’, native to modern day Eastern Siberia. We don’t know too much about them, but we know that they were nomadic, and probably had a lifestyle based on some combination of hunting and fishing. Around 15,000 BC, global sea levels were far lower, creating a land connection between Siberia and Alaska which the proto-Amerindians exploited to settle the continent. This is now accepted as the origin of most native American groups.

The second of these were the Proto-Dene, also native to modern day Eastern Siberia, around 6,400 BC. At this point, global sea levels had increased to almost modern levels, and walking between Siberia and Alaska had not been possible for thousands of years (since around 11,000 BC). However, the Proto-Dene nonetheless used canoes to make the crossing. Descendants of these migrants are found across Eastern Alaska, Western Canada, and the Southwestern United States to this day.

The third of these, and the final pre-Columbian contact to have a large impact on the local population, were the Paleo-Eskimo around 2500 BC. Yet another group from Eastern Siberia, they crossed the Bering Strait by Kayak to colonize the Alaskan coast. Unlike the Amerindians and Dene before them, the Paleo-Eskimos and their descendants did not settle deep inland, and their populations are mainly concentrated on the Alaskan and Northern Canadian coasts to this day. Perhaps their greatest impact on the societies of North and South America was the introduction of the Bow and Arrow, extremely useful for hunting and warfare alike.

While there were many small population exchanges between Siberia and Alaska in the following millennia, no future migration occured which drastically changed the societies of North America. But sometime between 700 AD and 1000 AD, the Polynesians became the first non-Siberian group to discover the Americas.

This was a very controversial theory for decades, and with good reason: A 50 mile voyage across the Bering Strait is reasonable with an ancient canoe, but a 2000 mile voyage from Rapa Nui to South America without a modern ship is crazy! The best known study into how this could have been accomplished was the Voyage of the Kon-Tiki in 1947. Norwegian navigator Thor Heyerdahl sailed from Peru to the Tuamotu Islands, an incredible distance of over 4000 miles, using technology available to. While the voyage did little in the way of proving contact, it did demonstrate that it was theoretically possible to sail between South America and Polynesia with primitive technology.

For decades, the main evidence for Polynesian-South American contact was on the name of the Sweet Potato. The Sweet Potato is a root vegetable native to the New World. High in calories and easy to grow, they became very widespread agricultural products across Central and South America. But when European explorers first documented the Polynesian islands, they found that Sweet Potatoes had been domesticated by Polynesian, indicating that they were traded between South America and the Polynesians. Even more convincingly, the names for Sweet Potato in Polynesian and South American languages are strikingly similar. Quechuan, the language of the Incan Empire, refers to the vegetables as ‘kumara’, ‘kumar’, ‘kumala’, or ‘kumal’, depending on local dialect. Rapa Nui, the language spoken by Polynesians on the island of Rapa Nui, refers to sweet potatoes as ‘kumara’, identically to the Quechuan word. (Douglas Yen, The Sweet Potato and Oceania, 1974)

Some historians still challenged the theory of Polynesian-South American contact, but this resistance has effectively gone extinct in the past decade, as genetic evidence has essentially proven not only contact, but South American settlement of Rapa Nui. While the population was primarily Polynesian descended as previously thought, a surprising amount of Native American ancestry was also found in the local population. This also lends some credence to Rapa Nui oral history saying that they had originated from land to the east, long written off by Europeans as a myth. (BA Lie et. al, Molecular genetic studies of natives on Easter Island, 2007) (J. Victor Moreno-Mayar et. al, Genome-wide Ancestry Patterns in Rapanui, 2014)

The timing of this contact remains in dispute, but the figure is typically placed in the late first millennium, as that is the time when sweet potatoes first appear in the Polynesian archaeological record and corresponds to the first arrival of Polynesian settlers on Rapa Nui.