D. It seems like the most reasonable answer. And there were also trading routes established during those times.
It led to recognition of post-traumatic stress as a legitimate psychological ailment
By exposing the citizen armies of Europe to prolonged and extreme
danger, World War One generated psychological casualties on an
industrial scale. This, in turn, created a military crisis that drew
doctors from a diverse range of specialties into the field of mental
health; never before had so much attention been focused on a single
psychiatric disorder.
Kansas City!! Hope this helps
B. Constitution
...is the answer to your question :)
