A national border would most likely have the most protection because nation's seek to prevent the import of illegal goods, movement of individuals into the country, and also to protect their borders against potential foreign invasion. Traditionally national borders would have more defenses, army, security forces, and police to protect the border than any of the rest of these borders.
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Answer:
The start of WWII. WWI was a very big cause of WWII. WWI led to depressions in Germany, Italy, the Soviet Union, and many more places which in turn caused powerful people to rise in many different countries. These countries in which a person of power rose each had some part in the start of WWII.
We were relieved by jobs, war, and other countries trade.