The mother country benefited under a mercantile system. A mercantile system is based on the benefit of the mother country's trade interests and manufacturers.
The main reason why the US joined the war was because multiple attack on passenger and merchant ships with submarine attacks .The final straw was when the RMS Lusitania by a German u-boat going to Liverpool England .
Answer:
Its B because it was clearly written at the time that it was happening.
