Idk I just needed the points
Started after World War 2
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.
Despite its reputation for brutal warfare, the Mongol Empire briefly enabled peace, stability, trade, and protected travel under a period of “Pax Mongolica,” or Mongol peace, beginning in about 1279 and lasting until the empire's end. But Genghis Khan's death in 1227 ultimately doomed the empire he founded.
Answer:
I guess after world War II
