Complex sentence: Access into North America was available between 20,000-11,000 years ago, after the Wisconsin glaciation had retreated but before the Bering land bridge became inundated by the sea, therefore haplogroup 1 was able to enter into North America during this period.
Split into simpler sentences: Access into North America was available between 20,000-11,000 years ago, after the Wisconsin glaciation had retreated but before the Bering land bridge became inundated by the sea. Therefore, haplogroup 1 was able to enter into North America during this period.