The Ice Age was a time on the earth when the waters of its oceans were trapped in ice caps near its poles. This in the peoples of the northern and, perhaps, southern hemispheres being forced to follow animals and other resources into more temperate terrain. In what would become Europe, this meant the farthest they could go was the western slopes of the coastal plains.
The Last Ice Age
According to most scientists, there have been many ice ages. However, all the others seem to have come a bit before mankind was around. Whatever the case, for all intents and purposes, the Ice Age that makes a difference is the one which affected the population and development of the civilization we all know and love. Sometime after the present continents got where they are today, something caused the floor of the Atlantic earth to crack open, forcing great mountains up towards the surface along with hot steam from a long range of underwater volcanoes. When this happened, snow began to fall nonstop on the poles and the mountain ranges of the earth.
The Great Migration
This not only forced the people in the northernmost parts of the world to move on to warmer climates, but it increased the coastlines all over the world as great amounts of water evaporated and were trapped in the new icecaps. It became nature's way of compensating humanity for the inconvenient truth of sudden climate change.
In Europe, the coastal plain of Europe saw an influx of scores of tribes, some from as far away as the Black Sea, following the herds of deer and other animals. They found that their new home was well worth the trip.
The upheaval of the Atlantic Ocean had created an unusual flow of warm water coming to the far north. Winters on the coast of what would become France were quite mild compared to those of the hinterlands. As a result, Forests began to grow on the coastal plain that became home for many subspecies of deer and smaller game, as well as migratory birds formerly known only for a few months in the summer. The northern tribes did not take well to the southern tribes that had come through the mountain passes between the Alps and the Pyranees. As a result, there was not much intermarriage (or, if you will, interbreeding). However, geneticists today have detected about 20% of the genome of France and the Netherlands does come from the Iberian Peninsula. Over the years, and way before the Roman Empire expanded westward, the ancient coastal population had ceased to be distinct from that of the continent. As time went by, the seas rose about 300 feet. Imperceptibly, what might have been ceased to matter. History continued on its way to the world we have today.