Answer:
C. Trench warfare
Explanation:
A's incorrect as alliances have existed for thousands of years
B's incorrect as an infantry charge's greatest weakness is the machine gun for obvious reasons
D's incorrect as both sides had machine guns, and was not the reason for victory.
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This leaves C, which makes sense as troops would be forced to hide on lower ground due to the deadliness of machine guns
To the Great Lakes is the the answer.
This is usually the result of an underdeveloped infrastructure or lack of technological achievements. The communication revolution requires countries to have highly advanced infrastructure that can support making a huge communications web and many countries have historically been destroyed by wars or have generally been poor and couldn't develop in that field, which means that nowadays they can't enter it quickly.
Keeping guns out of the hands of freed slaves
