The Bering Land Bridge was a land mass that connected Asia and North America during the last ice age. When the ice age ended, the sea levels rose and the Bering Land Bridge was flooded, cutting off the migration route from Asia to North America.
There is some evidence to suggest that there may have been other migrations from Asia to North America after the Bering Land Bridge was flooded. However, these migrations were much smaller and less significant than the initial migration that occurred during the last ice age.