Pre-Dorset fish hook
Several thousand years after the first people crossed the Bering Land Bridge into North America, other people came to North America by boats, crossing from Siberia across the Arctic Ocean to Alaska. This was about 7000-5000 BC. Archaeologists call these people the pre-Dorset Culture. They seem to have begun to leave Alaska about 4500 BC, when a warming period melted some of the Arctic ice, and they reached Greenland about 2500 BC. They hunted musk ox and reindeer in the north, and further south they hunted seal and caribou.
A second wave of people migrated into the Arctic from the west about 1000 BC. Archaeologists call these people the Dorset Culture, and the Inuit called them the Tuniit. These people were tall and strong, and they seem to have reached Greenland, on the Atlantic coast, about 500 BC. About 200 AD, the Tuniit seem to have abandoned Greenland again, and then around 1000 AD they began to migrate back south into Greenland, at first living mainly in the north and gradually moving south. The Arctic was getting warmer around 1000 AD, and maybe this made it harder for the Tuniit to find and hunt the animals they depended on for food.
Tuniit carving of a polar bear
The warmer weather melted the ice and made it easier for outsiders to invade Tuniit land. So about 1000 AD, the Tuniit people began to be conquered by a third wave of people who were moving east from Alaska along the Arctic Circle. These people called themselves the Inuit (some people call them the Eskimo, but that's an insulting Algonquin word for them). The Inuit seem to have reached the Atlantic coast by around 1400 AD. These Inuit people were shorter than the Tuniit, but they had big military advantages because they had dogs and boats, and apparently the Tuniit didn't. The Inuit hunted whales and used the meat to eat and the bones to build their houses.
About the same time, drawn by the warmer weather, Viking people also settled in Greenland. The first Vikings arrived in 986 AD, just as the Tuniit began to move southward into Greenland, and just as the Inuit began to move east.
But about 1350 AD this warmer weather ended and there was instead a period of colder weather called the Little Ice Age. Maybe because of this, the Vikings abandoned their last settlement in Greenland about 1408 AD, just as the Inuit conquered Greenland from the Tuniit.
At the same time, the Inuit moved into southern Greenland, maybe because the Little Ice Age forced them to move south in search of food. It got too icy in the northern Arctic to hunt whales anymore, and the Inuit were much poorer than they had been before. Instead of living in houses built out of sod (dirt) and whalebone, they had to move more and more often looking for food, and lived in tents or in igloos a lot of the time.
So the Inuit began to move gradually south, looking for places where there was more food to eat. By 1500 AD, the Inuit were beginning to move into southern Labrador, near Newfoundland (which is still pretty far north).