Answer:
During the Last Ice Age, many previously unconnected areas became connected by frozen ice bridges. This allowed people to migrate to new areas, often following migrating wild animals.
A famous example of this is the migration of East Asians from Siberia, to the American Continent. They crossed a frozen peninsula called Beringia (which does not exist anymore), arriving in Alaska. From there, they spread all over the American Continent in only 2,000 years.