Discovery of America
The discovery of America (in the sense of there thereafter being continuous contacts between the Americas and Eurasia/Africa) occurred in 1492 by Christopher Columbus.
The Vikings had briefly been in North America ("Vinland") around 1000 AD and the Amerindians had colonized the Americas long before this. In addition there are various theories on other early contacts as discussed in the articles on the Amerindians and the Solutrean hypothesis.
