What timeline? Did you post it?
They are called the tectonic plates... that's what causes earthquakes.
The Soviet Union, like any complex nation, is intertwined upon itself.
When elements of the Soviet Union began to fall, notably its economic system, it could no longer supports its citizenry. While this was not a problem in the 20s and 30s, the people of the Soviet Union knew how people were living outside of the Soviet Union and the allure of communism was no longer enough to keep their bellies full at night.
So, as elements failed like the currency it triggered reactions in every other sector of the Soviet system.
Answer: Mountains in Mexico
Explanation:
Mexico has several mountains owing to it having two very prominent mountain ranges known as the Sierra Madre Occidental and the Sierra Madre Oriental. These mountains were big hindrances to travel across Mexico.
Mexico City sits on the confluence of these two great ranges which means that any trade overland to and from Mexico City would have to go over mountains and this shows that trade might have been difficult.