Tectonic direction of NA = SW. Chicago was inside the Arctic Circle possibly 30 mil years ago - a guess.
Greenland is today's exhibit of an ice age. The middle of Greenland went ice age 400-800k years ago, but it started at the northern tip, which was completely green 2 million years ago. On the tail end outside of the Arctic Circle, the Vikings farmed the southern tip of Greenland until 1400s when the ice age advanced to cover Greenland completely. Ice obviously melts outside of the Arctic Circle, but the "glacier manufacturing system" is the land within 600 miles of the pole. Alaska is not in ice age because it is not that close to the Pole, but is in the Arctic Circle. AA also demonstrates a continent specific ice age will drive glaciers right out of the polar circle.