The mankind from the moment of the emergence sought to develop new lands. Search of new habitats became one of powerful engines of progress. However methods of development of territories differed during different eras.
Primitive times
Hunting and collecting due to which there lived the mankind before transition to settled lifestyle meant that in one territory there could be strictly limited number of people. When resources ceased to be enough a part of the population, they passed to the new place. Thus the mankind was settled from Africa practically worldwide.
Rather simple and clear looks resettlement to Eurasia, but how people got to America? Apparently, during an era of resettlement of the Bering Strait did not exist, and people could pass from Chukotka to Alaska by land. However it should be noted that at resettlement on other islands and continents the separate groups of people quite often turned out isolated that led to formation of new races.
Opening at the time of the Ancient World and the Middle Ages
With development of a civilization the people began not just to move on new lands, but also quite often to capture them, attaching to already existing states. The mankind became more mobile thanks to emergence of navigation. Began to create also the first cards on which lands known to people were displayed. Though Columbus is considered the pioneer of America, historians proved that for the first time Europeans visited this continent in the 10th century. Vikings could land on east coast of Canada. Also archeological excavations showed that not only Vikings visited the American territories, but also Indians were in Scandinavia, coming there by the European ships.
After decline of an era of Vikings the contacts with the American continent were lost, and by the time of Columbus's swimming this continent was not known.
Great geographical discoveries
In the 15th century the Europeans expanded the horizons even more. Colonization of the whole continents which quite often took place by rather cruel methods - with reduction of local community and sending them in the reservation began. At the same time Europeans thanks to new opening could change life and in the Old World - from America many crops which improved a food situation in Europe were brought.
It is interesting to note that riches. America received at gain, not always did well - Spain which got access to a large amount of gold several times appeared the bankrupt because of inflation.
At the time of Great geographical discoveries the first rather accurate maps of Earth appeared, however only with discovery of Antarctica the picture of the world became really full. However a number of opening had and for the 19-20th centuries - it were already the discoveries made by ethnographers, they concerned some isolated earlier African tribes.