The Americas from what is known and discovered till now are by far the latest continents that were settled by the people. Even though it is still not clear when exactly did this happened it is in the range between 19,000 and 12,000 years ago as the biggest given and lowest given number by scientists. It is understandable though that people found it hard to migrate in this part of the world since it was cut of by an ocean and the only way that they could migrate was through the Bering Land Bridge which in fact was an icy bridge between the continents and extremely inhospitable place. There is also the large carnivores in North America as a factor that delayed the migration, and of course the ongoing ice age which covered huge portions of North America with glaciers, ice and snow.
I believe that it was the Americas (Actually, it was more probably Pacific Islands, but those are not an option): South America was colonized as recently as 12 000 years ago.
