Answer:
In conclusion many things caused tension between the US and the Soviet Union. The extreme mistrust of one another. The threat of Nuclear warfare. The soviets trying to spread communism.
The 100 year period peace and prosperity is Pax Romana.
Because it was when we started to expand our territories
City dwellers could visit museums could be a statement that describes a cultural opportunity that became available as cities grew in the late 1800s. Hope this helps!