Weather will be the primary reason. Despite its huge size. the real habitable area is probably less than 10% of its geographical size. Even Southern Ontario is deemed by many I know to be "too cold to live". 90% of Ontario and Quebec are simply inhabitable. I also personally think the entire Manitoba and Saskachewan are not suitable for human habitation unless we can create a way to simply hibernate during the 6 month winter (why there are so few people in Montana and North Dakota?) The fact that Montreal are thrive as a vibrant metropolis is already sort of a miracle and we don't see many such large cities with such severe weather. The only other case I can think of is probably Moscow.
<span>Religion, at that time, was governed by the State. In such, the government controlled all aspects of religious life and what sorts of materials would pass muster as being "proper" and what viewpoints would be considered "non-threatening" to the health of the nation. Any belief systems that were outside of this were considered verboten.</span>
One such sentence could be this: "Some of the earliest humans who ever lived were nomads, who would roam around the land in search of food. Many of them migrated North, out of Africa and into Europe."
An encyclopedia would be the best source.
