Railroads played an absolutely crucial role in the Industrial Revolution, since they made for the incredibly fast transfer of goods such as iron and steel that were used to build things--not to mention the transport of the workers themselves.
1. It never lead to a single large conflict. Rather many smaller ones.
2. During the Cold War, the USA and USSR both funded army’s of smaller countries to fight for them. For instance the Korean and Veitnam Wars.
3. The Cold War came to a close when the Soviet Union dissolved in 1991.
Hunter-Gatherers is the answer to your question<span>
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